Laser system

ABSTRACT

A method and apparatus may comprise a line narrowed pulsed excimer or molecular fluorine gas discharge laser system which may comprise a seed laser oscillator producing an output comprising a laser output light beam of pulses which may comprise a first gas discharge excimer or molecular fluorine laser chamber; a line narrowing module within a first oscillator cavity; a laser amplification stage containing an amplifying gain medium in a second gas discharge excimer or molecular fluorine laser chamber receiving the output of the seed laser oscillator and amplifying the output of the seed laser oscillator to form a laser system output comprising a laser output light beam of pulses, which may comprise a ring power amplification stage.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.12/987,039, filed Jan. 7, 2011 and entitled LASER SYSTEM, which is acontinuation of U.S. application Ser. No. 11/787,180, filed on Apr. 13,2007 and entitled LASER SYSTEM, which is a continuation-in-part of U.S.application Ser. No. 11/584,792, filed on Oct. 20, 2006, entitled LASERSYSTEM, now abandoned, which is a continuation-in-part of U.S.application Ser. No. 11/521,904, filed Sep. 14, 2006, entitled LASERSYSTEM, now abandoned; U.S. application Ser. No. 11/522,052, filed Sep.14, 2006, entitled LASER SYSTEM, now abandoned; U.S. application Ser.No. 11/521,833, filed Sep. 14, 2006, entitled LASER SYSTEM, nowabandoned; U.S. application Ser. No. 11/521,860, filed Sep. 14, 2006,entitled LASER SYSTEM, now abandoned; U.S. application Ser. No.11/521,834, filed Sep. 14, 2006, entitled LASER SYSTEM, now abandoned;U.S. application Ser. No. 11/521,906, filed Sep. 14, 2006, entitledLASER SYSTEM, now abandoned; U.S. application Ser. No. 11/521,858, filedSep. 14, 2006, entitled LASER SYSTEM, now abandoned; U.S. applicationSer. No. 11/521,835, filed Sep. 14, 2006, entitled LASER SYSTEM, nowabandoned; and U.S. application Ser. No. 11/521,905, filed Sep. 14,2006, entitled LASER System, now abandoned; which applications and thepresent application claim priority to U.S. Application No. 60/732,688,filed on Nov. 1, 2005, entitled 200 W GAS DISCHARGE EXCIMER OR MOLECULARFLUORINE MULTICHAMBER LASER, and to U.S. Application No. 60/814,293filed on Jun. 16, 2006, entitled 200 WATT DUV GAS DISCHARGE LASERSYSTEM, and to U.S. Application No. 60/814,424, filed on Jun. 16, 2006,entitled LONG LIVED MO IN MOPO CONFIGURED LASER SYSTEM, the disclosuresof each of which are hereby incorporated by reference. The presentapplication is also related to the applications referenced in the abovenoted co-pending and co-filed patent applications, the disclosures ofwhich referenced applications are also hereby incorporated by reference.

FIELD OF THE SUBJECT MATTER DISCLOSED

The subject matter disclosed is related to high power gas dischargelaser systems for DUV light sources, e.g., used in integrated circuitphotolithography or other laser treatment applications such as laserannealing for low temperature poly-silicon processing (“LTPS”), such asthin beam sequential lateral solidification (“tbSLS”).

BACKGROUND

Deep ultraviolet light sources, such as those used for integratedcircuit photolithography manufacturing processes have been almostexclusively the province of excimer gas discharge lasers, particularlyKrF excimer lasers at around 248 nm and followed by ArF lasers at 198 nmhaving been brought into production since the early 90's, with molecularfluorine F₂ lasers also having also been proposed at around 157 nm, butas yet not brought into production.

To achieve resolution reduction at a fixed wavelength and fixed NA(i.e., an 193 nm XLA 165 on a XT:1400 with an NA of 0.93), one mustoptimize k1, where k1 represents process-dependent factors affectingresolution.

Based on Rayleigh's equation, for dry ArF tools today smaller resolutionof state-of-the-art high-numerical-aperture ArF lithography can only beachieved with Resolution-Enhancement Techniques (RET's). RETs are acost-effective way to maintain the aggressive evolution to smallerdimensions in IC manufacturing and are becoming integral tomanufacturing lithography solutions.

These Process-related resolution enhancement efforts (lowering k1) havefocused on reticle design, using methodologies such as phase shifting orpattern splitting on dual masks. While these techniques improve imaging,they also have significant drawbacks, including throughput loss. So whenk1 is optimized for an application the only way to improve resolutionfurther is to go back to the wavelength or NA.

Immersion lithography does just this for the 45 nm, the wavelength isconstant at 193 nm so introducing water allows for NA's up to 1.35 andthis relaxes the k1 requirement until processing at the 32 nm isrequired.

Since first introduction of excimer laser light sources in the DUVwavelength manufacturers of these light sources have been under constantpressure not only to reduce the wavelength, but also to increase theaverage power delivered to the wafer in the manufacturing processcarried out by the steppers and scanners of the principle customers forsuch light sources, the stepper/scanner manufacturers, now includingCanon and Nicon in Japan and ASML in the Netherlands.

This requirement for smaller and smaller wavelength has come from theneed of the integrated circuit manufacturer customers for thestepper/scanner makers to be able to print smaller and smaller criticaldimensions on the integrated circuit wafers. The need for higher powerhas generally been driven by either the need for more throughput orhigher dose for exposing certain photo resists on the wafer, or both.

This steady progression down the road formed by the so-called Moore'slaw about the progression of integrated circuit capabilities, and thus,the number of transistors per unit area and thus also basically smallerand smaller critical dimensions, has created various and seriousproblems for the light source manufacturers to address. Particularly themove to the 193 nm wavelength node of light sources has resulted inseveral challenges.

The lower wavelength photons from an 193 nm laser system has havinghigher energies than the prior KrF 248 nm light sources has causedproblems both for the light source manufacturers and the present dayscanner manufacturers. Regions in both the light source and scannerreceiving these higher energy photons, particularly at high energydensity levels per unit area have been required to be made of what iscurrently the single window/lens material that can stand up to theseoptically damaging photons for any reasonably economical period of time,i.e., CaF₂. Such single material lenses in the scanners have requiredthe scanner manufacturers to, e.g., demand virtually monochromatic lightout of the laser light source systems, e.g., to avoid chromaticaberrations in the lenses.

The demand for smaller and smaller bandwidths (more and moremonochromatic light) has required more and more precisely sensitive linenarrowing units, e.g., containing etalon or grating line narrowingoptical elements. Older style single chamber laser light sourcessuffered from short life of such line narrowing units because, amongother things, much of the light entering the line narrowing unit is lostin the line narrowing process, the narrower the output bandwidth beingrequired the larger the loss. Thus, the requirement was to send higherand higher pulse energy into the line narrowing unit in order to get agiven pulse energy out of the laser system. Thus, e.g., formerlyutilized single chamber ArF laser systems were capable of laser outputpulses of around 5 mJ with reasonably cost effective lifetimes for theline narrowing units.

A first approach of the light source manufacturers, among other things,to address these issues with ArF light sources to get progressivelynarrower bandwidths and higher output average power was to increasepulse repetition rate, with essentially the same pulse energy per pulse.Thus through about 2002 pulse repetition, rates increased from hundredsof pulses per second to 4 kHz. This kept the optical damage per pulsedown, but increased the overall exposure of the laser optics in the linenarrowing units and elsewhere as the pulse repetition rate increased. Inaddition, higher pulse repetition rates created other problems for thelight source manufacturers, principal of which were, e.g., increasedelectrode deterioration rates and requirements for faster gascirculation rates within the lasing chamber, i.e., requiring more fanmotor power and adding more heat to the chamber and the fan motor andbearing assembly, resulting in reductions in mean time betweenreplacement for the lasing chambers.

Higher pulse repetition rates also caused problems that the light sourcemanufacturers had to address, e.g., in the magnetic switched pulse powersupplies with timing and component lifetimes negatively impacted by thehigher thermal loads, e.g., on the magnetic switching elements in thepulsed power system at the higher pulse repetition rates.

To add to the difficulties to be addressed by the light sourcemanufacturers the integrated circuit have also continued to demandimprovements in other laser pulse parameters, e.g., beam profile andbeam divergence and pulse-to-pulse stability requirements, e.g., forbandwidth and energy and timing from the trigger signal from thescanner, etc. The ability to provide the various controls of the laseroutput and operating parameters of this nature can be negativelyimpacted by either or both of increased pulse energy demands and higherpulse repetition rate, along with variations in such things as the dutycycle (percentage of time the laser is firing) during operation), pulseenergy selected by the scanner, rates of depletion of F₂ in the lasingchamber, etc.

For example the applicant's assignee's product the ELS-6010, The world'sfirst variable 248 nm KrF excimer single chamber laser system,introduced in the late nineties, provided what was then advanced opticalperformance applicable to 130 nm node of semiconductor manufacturing. Itprovided what was then also a highly line-narrowed bandwidth of about0.5 pm at full-width half-maximum (FWHM) and about 1.4 pm (95% energyintegral), thus enabling lithography steppers and scanners to achievefull imaging performance using lenses with numerical apertures of >0.75.The ELS-6010 supported higher throughput rates for its day, e.g.,operating at up to 2.5 kHz, 8 mJ pulse energy, for 20 W average power,the ELS-6010 also delivered what was then improved dose stability at thewafer for better CD control and higher yield. The ELS 6010 also providedfor precise energy control to reduce the need for attenuation, optimizepulse usage, and extended the useful lifetime of laser consumables.Improvements to signal processing components in the wavelengthstabilization module provided faster data acquisition and more reliablewavelength stability.

The ELS 6XXX models were followed by a later model, called byapplicant's assignee the ELS 7000, addressing even more aggressiverequirements of the semiconductor industry for the sub-130 design node.This also KrF 248 nm wavelength excimer single chamber laser systemdelivered even more tightly constricted bandwidth at higher power inorder to reduce CD geometry in semiconductor photolithography, furtherimproving throughput, and reducing operating costs. The 7000 was alsomade available in an ArF 193 nm wavelength version. More average powerwas delivered by increasing pulse repetition rate from 2.5 kHz to 4 kHz.The 7010 added improved line narrowing performance (selecting bandwidth)and wavelength stabilization, e.g., to insure better focus control,maximize exposure latitude, and improve semiconductor circuit criticaldimension (“CD”) control. Improvements were also made in the gasinjection algorithm, e.g., for injecting small, precise amounts of gasinto the laser chamber during exposure sequences to provide superiorenergy stability. The ELS-7000 was aimed to meet the requirements ofhigh volume product of sub-0.13 micron devices on 248 nm exposure tools.Offering 4 kHz, 7.5 mJ, 30 W optical output, plus the same ultra-lowbandwidth performance as the 6010, and high-speed wavelength control,the ELS-7000 also reduced laser consumables costs.

The ELS 7000 was followed in about 2001 by applicants' assignee's ELS7010 model that further aggressively addressed the performance and costrequirements of the semiconductor industry for the sub-100 nm designnodes. The ELS-7010, also a 4-kHz krypton fluoride (KrF, 248 nm),excimer light source addressed the demands of the photolithography bythe semiconductor industry for sub-100 nm design nodes. The ELS-7010offered further increased power and bandwidth performance parameters forKrF light sources and still further decreased the cost of consumables(CoC). The ELS-7010 provided a 50 to 100 percent improvement on theexpected life of each of the major consumable modules, while at the sametime increasing power and further reducing bandwidth. The ELS 7010 was a4 kHz, 10 mJ, 40 W, (FWHM) 0.35 pm and (E95%) 1.2 pm, single chamberlaser system

Another follow on, and probably the further extent of single chamberexcimer laser technology was applicants' assignee's Nanolith 7000 ArF(193 nm) single chamber laser system introduced in about 2002. TheNanolith 7000 was an ArF laser system with about the same bandwidthspecifications at 193 nm as the ELS 7000, i.e., ≦0.5 pm FWHM and ≦1.3 pm(E 95% intensity integral) at 5 mJ and 4 kHz (20 Watt) operation topower next-generation lithography tools with superior spectral power andhighly focused line-narrowed bandwidth, while again reducing laserconsumable costs, a more difficult task at 193 nm, due mostly toincreased optical damage resulting from the reduced wavelength light.The 193 nm Nanolith ArF light source for volume photolithographysemiconductor manufacturing, with its highly line-narrowed, high powerand high accuracy tuned wavelength control enabled the most advancedimaging of that time, e.g., with NA>0.75 below the 100 nm node, stillmeeting the then current such other requirements as image contrast andwafer throughput, enabling chip design to shrink even further,accommodating, e.g., faster processor speed, larger memory capacity perchip, and at the same time better yield per wafer.

Featuring, e.g., a new chamber design, the NanoLith 7000 incorporatednew technological advances in power design, laser discharge chamber, andwavelength control to enable tight control of exposure dose energy(<±0.3%) and laser wavelength stability (<±0.03 pm). On-Board lasermetrology provided pulse-to-pulse data acquisition and feedback controlto minimize transient wavelength instabilities, thereby enhancingexposure process latitude and CD control.

However, as even further demands for shrinking bandwidth and increasedpower moved even beyond the technological advances of applicant'sassignees world-class single chamber laser systems, it became clear thatsomething would have to replace the single chamber system. Furtheroptimizing such beam parameters as bandwidth, including keeping itwithin some specific range, e.g., for OPC reasons, rather than just anot to exceed specification, was becoming impossible at the necessaryaverage power levels. At the time, it was also deemed that increasingrepetition rate was not the effective path to take for a number ofreasons.

Applicant's assignee's chosen solution was a two chambered laser systemcomprising a seed laser pulse beam producing laser chamber, e.g., amaster oscillator (“MO”), also of the gas discharge excimer variety,seeding another laser chamber with an amplifying lasing medium, also ofthe same excimer gas discharge variety, acting to amplify the seed beam,a power amplifier (“PA”). Other so-called master oscillator-poweramplifier (“MOPA”) laser systems had been known, mostly in the solidstate laser art, essentially for boosting power output. applicants'assignee came up with the concept of the utilization of seed laserchamber in which a seed laser was produced, with the view of optimizingthat chamber operation for selecting/controlling desirable beamparameters, e.g., bandwidth, beam profile, beam spatial intensitydistribution, pulse temporal shape, etc. and then essentially amplifyingthe pulse with the desirable parameters in an amplifier medium, e.g.,the PA. This breakthrough by applicants' assignee was able to meet thethen current demands attendant to the continually shrinking node sizesfor semiconductor photolithography DUV light sources.

The first of these two chamber laser systems was the XLA-100, providingleading edge optical and power performance in an ultra line narrowed,high power argon fluoride (ArF) production light source. The dualchamber Master Oscillator Power Amplifier (MOPA) architecture developedby applicants' assignee, was capable of 40 W of average output power,double the output power of Cymer's earlier, single chamber-basedNanolith 7000 ArF models, while also meeting even increasingly stringentperformance and cost requirements necessary for semiconductor chipproduction at the <100-nm node. Providing an ultra line-narrowedspectral bandwidth of about 0.25 pm FWHM, and about 0.65 pm E95%integral, the tightest spectral bandwidth performance of anydeep-ultraviolet (DUV) production light source up to that time, i.e.,about 2003, the XLA 100 provided the light that enabled high contrastimaging for lithography tools with an numerical aperture (NA) up to 0.9.

This was mostly because less energy was wasted in the MO chamber inproducing the beam with selected optical parameters, e.g., bandwidth,and the amplifier medium provided plenty of amplification to get anoutput of the MO at about, e.g., 1 mJ up to a PA output of 10 mJ, 40watts average output power at 4 kHz operating pulse repetition rate.This allowed, e.g., fewer pulses per exposure window, e.g., enabling theuse of less pulses per exposure. The same tight exposure controls wereavailable, i.e., exposure dose (about ±0.3 percent) and wavelengthstability (about ±0.025 pm) by providing pulse-to-pulse data acquisitionand feedback control to its in-situ metrology system, involving samplingat the outputs of both the MO and PA.

In about the end of 2005 applicants' assignee introduced the XLA-200, asecond generation two chamber XLA laser system which became the world'sfirst immersion photolithography enabling gas discharge laser lightsource even further reduced the ultra line narrowed output at 50% moreaverage output power than the original XLA-100 series. In a quest forsmaller feature sizes, new and innovative technologies were needed tomeet the mandate of Moore's law and the concomitant ever smaller CDsizes, especially with extreme ultraviolet sources (EUV”) delivery datesbeing moved out to the end of the first decade of the new millennium orfurther. The introduction of a fluid of different refraction index thanair, e.g., water, to the exposure process, known as ImmersionLithography, was becoming a cost-effective and production-viabletechnique for extending 193 nm wavelength lithography technologies tomeet sub-65 nm process nodes, i.e., ultra-high numerical aperture (NA),immersion-scanner systems.

The XLA 200 met stringent performance and cost requirements necessaryfor the most sophisticated semiconductor chip productiontechniques-providing ultra-pure spectral performance of about 0.12 pmFWHM and 0.25 pm E95% integral-to support the ultra-high NA scannersystems required for sub-65 nm exposure, while simultaneously providinghigh power, (up to 60 W), to support the industry's high productivityneeds. Leading edge spectral metrology, used in the XLA series, alsoenabled monitoring and maintaining the very high spectral purity,including on-board high-accuracy E95% intensity integral bandwidthmetrology, e.g., for providing the process control needed for immersionlithography technologies. The XLA 200 was a 193 nm, 4 kHz, 15 mJ, 60 Wtwo-chamber laser system.

Subsequently applicants' assignee introduced in about early 2006 the XLA300, a 6 kHz 90 W version of the XLA 200. For 193 nm immersionlithography has emerged as the leading for the critical layer processingdown to the 32 nm node XLA 300 meet the requirements. Even at the 45 nmnode, requirements for critical dimensions, profiles, line edgeroughness and overlay requirements of different layers impact designmargin and limit yield. High throughput hyper NA (>1.2) exposure toolsalong with polarized illumination effects and optimized ResolutionEnhancement Techniques (RET) will be required for process control, whichcan be met only by the introduction of applicants assignee's XLA 300series laser systems. With the k1 physical limit at 0.25 (for memoryapplications <0.30 is aggressive, logic is usually higher), for 45 nmprocessing high NA exposure tools and high spectral power (high laserpower & high spectral purity) lasers are required. This is what theapplicants; assignee's XLA 300 series of lasers currently delivers.

Unfortunately, Moore's law is not done and EUV is still a developmentproject. Therefore addressing even higher power requirements for 193 nmlaser light sources is required. Two major obstacles to the typicalpulse repetition rate increases evidenced in the advancement of poweroutput in the above noted single chamber laser systems and later twochamber laser systems is the difficulty of getting excimer gas dischargelaser system chambers to operate at above 6 kHz and the increasedoptical damage to certain optical components exposed to the most severedoses of 193 nm light during operation as the pulse repetition rate goeseven higher, even with the MOPA architecture. In addition, for variousreasons, including the higher pressure operation of the MO's needed,e.g., to extract as much pulse energy as possible out of the linenarrowed MO chamber, e.g., around 380 kPa total gas pressure, with,e.g., around a maximum of about 38 kPa of fluorine partial pressurecaused conditions advantageous to longer chamber lifetimes to not beattainable, which along with LNM lifetime issues was contributing to theincrease in CoC of XLA laser systems.

This latest generation MOPA-based Argon Fluoride light source canprovide an ultra-line narrowed bandwidth as low as 0.12 pm FWHM and 0.30pm 95% energy integral laser light source supporting very high numericalaperture dioptric and catadioptric lens immersion lithography scanners.The XLA 300 introduces an extendable 6 kHz platform to deliver 45 to 90W of power. Increased repetition rate, along with pulse stretching,minimizes damage to the scanner system optics. State-of-the-art on-boardE95% bandwidth metrology and improved bandwidth stability to provideenhanced Critical Dimension control. Longer chamber lifetimes and provenpower optics technology extends the lifetime of key laser modules toimprove (reduce) CoC (Cost of Consumables), through, e.g., longerchamber lifetimes and proven power optics technology that extends thelifetime of key laser modules.

In the area of simply generating high average power, e.g., around 100 wand above and up to even 200 w and above, with laser systems operatingat not much greater than 6 kHz, the MOPA system, eliminating the linenarrowing from the required architecture for the MO still requires newtechnology.

One possible solution is to use an amplifying medium that comprises apower oscillator. The PA of applicants' assignee is optimized both foramplification and for preservation of the desirable output beam pulseparameters produced in the MO with optimized, e.g., line narrowing. Anamplifier medium that is also an oscillator, a power oscillator (“PO”),has been proposed and used by applicants' assignee's competitorGigaPhoton, as evidenced in U.S. Pat. No. 6,721,344, entitled INJECTIONLOCKING TYPE OR MOPA TYPE OF LASER DEVICE, issued on Apr. 13, 2004 toNakao et al; U.S. Pat. No. 6,741,627, entitled PHOTOLITHOGRAPHICMOLECULAR FLUORINE LASER SYSTEM, issued on May 25, 2004 to Kitatochi etal, and U.S. Pat. No. 6,839,373, entitled ULTRA-NARROWBAND FLUORINELASER APPARATUS, issued on Jan. 4, 2005 to Takehisha et al.

Unfortunately the use of an oscillator such as with front and rearreflecting mirrors (include a partially reflecting output coupler, andinput coupling, e.g., through an aperture in one of the or through,e.g., a 95% reflective rear reflector) has a number of drawbacks. Theinput coupling from the MO to the amplifier medium is very energyloss-prone. In the amplifier medium with such an oscillator cavityoptimized beam parameters selected, e.g., in the MO chamber, may bedenigrated in such an oscillator used as an amplifying medium. Anunacceptable level of ASE may be produced.

Applicant's propose an architecture that can preserve the optimized beamparameters developed in an MO chamber almost to the same degree asapplicants' assignee's present XLA XXX systems, while producing muchmore efficient amplification from the amplification medium, e.g., togive current levels of output average power with strikingly reducedoutput pulse energy from the MO (seed laser) resulting in, e.g., a muchlower CoC for the MO. Further, applicants believe that according toaspects of embodiments of the subject matter disclosed, e.g.,pulse-to-pulse stability or a number of laser output parameters can alsobe greatly improved.

Increased Wafer Throughput & Productivity maintaining the advancingrequirements for Deep Ultra Violet lithography in mass production, andincreasing importance on the economics of the laser use is satisfied inpart by increasing the laser's repetition rate to 6 kHz and output powerto 90 W. Resolution and critical dimension (CD) control in advancedlithography, at the 193 nm, requires a narrow spectral bandwidth, e.g.,because all lens materials have some degree of chromatic aberration,necessitating a narrow bandwidth laser to reduce the wavelengthvariation in the light source, thereby diminishing the impact ofchromatic aberration. Very narrow bandwidth can improve the ultimateresolution of the system, or, alternatively can give lens designers morefocal latitude. Expensive calcium fluoride optics suffer less chromaticaberration at 193 nm than fused silica does. Narrow bandwidth lasersreduce the need for calcium fluoride optics in 193 nm exposure systems.Spectral engineering, e.g., for critical dimension (CD) control, e.g.,driven by more aggressive use of optical proximity correction and higherNA lenses increased the sensitivity to BW and BW changes, including notjust bandwidth specification of not to exceed, but bandwidthspecification of within a relatively narrow range between a high (theformerly not to exceed type of limit) and a low. Stable BW is even moreimportant for ArF than it has been for KrF. Even a very low BW can yieldpoor CD if exhibiting significant variations underneath the upper limit.Thus, both BW metrology and BW stabilization are critical technologiesfor good CD control.

A 6 kHz Repetition Rate results also in improved dose performance tominimize CD variation at the 45 nm node, which can reduced dosequantization errors, e.g., that occur when the exposure slit does notcapture all pulses in the dose. In addition, dose errors due to laserbeam dynamics can cause imperfections of the exposure slit profile. Anewly designed LNM for the XLA 300, e.g., uses a higher resolutiondispersive element and an improved wavelength control actuationmechanism, which improved LNM in combination with applicant's assignee'sReduced Acoustic Power (RAP) chamber provides excellent stability ofbandwidth.

Other problems exist in such arrangements, e.g., ASE production can besignificant enough, e.g., in the power amplification stage to causedownstream problems in the line narrowed versions, because the ASE isout of band. The ASE may also cause problems in the, e.g., broadband,e.g., LTPS versions, since the beam treatment optics, e.g., to producean elongated and very thin, e.g., 10μ or so wide, beam may be sensitiveto light well out of the broadband normally produced by excimer lasingin the amplification stage. In addition, ASE can rob gain medium andthus lower the available in-band or otherwise useable output of theamplification stage.

Buczek, et al, CO₂ Regenerative Ring Power Amplifiers, J. App. Phys.,Vol. 42, No. 8 (July 1971) relates to a unidirectional regenerative ringCO₂ laser with above stable (conditionally stable) operation anddiscusses the role of gain saturation on CO₂ laser performance. Nabors,et al, Injection locking of a 13-W Nd:YAG ring laser, Optics Ltrs., vol.14, No 21 (November 1989) relates to a lamp-pumped solid-state CW ringlaser injection locked by a diode-pumped solid state Nd:YAG masteroscillator. The seed is input coupled into the ring laser by a half-waveplate, a Faraday rotator and a thin film polarizer forming an opticaldiode between the seed laser and the amplifier. Pacala, et al., Awavelength scannable XeCl oscillator-ring amplifier laser system, App.Phys. Ltrs., Vol. 40, No. 1 (January 1982); relates to a single passexcimer (XeCl) laser system seeded by a line narrowed XeCl oscillator.U.S. Pat. No. 3,530,388, issued to Buerra, et al. on Sep. 22, 1970,entitled LIGHT AMPLIFIER SYSTEM, relates to an oscillator laser seedingtwo single pass ring lasers in series with beam splitter input couplingto each. U.S. Pat. No. 3,566,128, issued to Amaud on Feb. 23, 1971,entitled OPTICAL COMMUNICATION ARRANGEMENT UTILIZING A MULTIMODE OPTICALREGENERATIVE AMPLIFIER FOR PILOT FREQUENCY AMPLIFICATION, relates to anoptical communication system: with a ring amplifier. U.S. Pat. No.3,646,468, issued to Buczek, et al. on Feb. 29, 1972 relates to a lasersystem with a low power oscillator, a high power oscillator and aresonance adjustment means. U.S. Pat. No. 3,646,469, issued to Buczek,et al. on Feb. 29, 1097, entitled TRAVELLING WAVE REGENERATIVE LASERAMPLIFIER, relates to a laser system like that of the '468 Buczek patentwith a means for locking the resonant frequency of the amplifier tofrequency of the output of the oscillator. U.S. Pat. No. 3,969,685,issued to Chenausky on Jul. 13, 1976, entitled ENHANCED RADIATIONCOUPLING FROM UNSTABLE LASER RESONATORS relates to coupling energy froma gain medium in an unstable resonator to provide a large fraction ofthe energy in the central lobe of the far field. U.S. Pat. No.4,107,628, issued tot Hill, et al., on Aug. 15, 1978, entitled CWBRILLOUIN RING LASER, relates to a Brillouin scattering ring laser, withan acousto-optical element modulating the scattering frequency. U.S.Pat. No. 4,135,787, issued to McLafferty on Jan. 23, 1979, entitledUNSTABLE RING RESONATOR WITH CYLINDRICAL MIRRORS, relates to an unstablering resonator with intermediate spatial filters. U.S. Pat. No.4,229,106, issued to Domschner on Oct. 21, 1980, entitledELECTROMAGNETIC WAVE RING GENERATOR, relates to a ring laser resonatorwith a means to spatially rotate the electronic field distribution oflaser waves resonant therein, e.g., to enable the waves to resonate withopposite polarization. U.S. Pat. No. 4,239,341 issued to Carson on Dec.16, 1980, entitled UNSTABLE OPTICAL RESONATORS WITH TILTED SPHERICALMIRRORS, relates to the use of tilted spherical mirrors in an unstableresonator to achieve asymmetric magnification to get “simultaneousconfocality” and obviate the need for non-spherical mirrors. U.S. Pat.No. 4,247,831 issued to Lindop on Jan. 27, 1981, entitled RING LASERS,relates to a resonant cavity with at least 1 parallel sided isotropicrefracting devices, e.g., prisms, with parallel sides at an obliqueangle to part of light path that intersects said sides, along with ameans to apply oscillating translational motion to said refractingdevices. U.S. Pat. No. 4,268,800, issued to Johnston et al. on May 19,1981, entitled, VERTEX-MOUNTED TIPPING BREWSTER PLATE FOR A RING LASER,relates to a tipping Brewster plate to fine tune a ring laser locatedclose to a flat rear mirror A acting as one of the reflecting optics ofthe ring laser cavity. U.S. Pat. No. 4,499,582, entitled RING LASER,issued to Karning et al. on Feb. 5, 1980, relates to a ring laser systemwith a folded path pat two separate pairs of electrodes with a partiallyreflective input coupler at a given wavelength. U.S. Pat. No. 5,097,478,issued to Verdiel, et al. on Mar. 17, 1992, entitled RING CAVITY LASERDEVICE, relates to a ring cavity which uses a beam from a master laserto control or lock the operation of a slave laser located in the ringcavity. It uses a non-linear medium in the cavity to avoid the need ofinsulators, e.g., for stabilizing to suppress oscillations, e.g., asdiscussed in Col 4 lines 9-18. Nabekawa et al., 50-W average power,200-Hz repetition rate, 480-fs KrF excimer laser with gated gainamplification, CLEO (2001), p. 96, e.g., as discussed with respect toFIG. 1, relates to a multipass amplifier laser having a solid state seedthat is frequency multiplied to get to about 248 nm for KrF excimeramplification. U.S. Pat. No. 6,373,869, issued to Jacob on Apr. 16,2002, entitled SYSTEM AND METHOD FOR GENERATING COHERENT RADIATION ATULTRAVIOLET WAVELENGTHS, relates to using an Nd:YAG source plus anoptical parametric oscillator and a frequency doubler and mixer toprovide the seed to a multipass KrF amplifier. U.S. Pat. No. 6,901,084,issued to Pask on May 31, 2005, entitled STABLE SOLID STATE RAMAN LASERAND A METHOD OF OPERATING SAME, relates to a solid-state laser systemwith a Raman scattering mechanism in the laser system oscillator cavityto frequency shift the output wavelength. U.S. Pat. No. 6,940,880,issued to Butterworth, et al. on Sep. 6, 2005, entitled OPTICALLY PUMPEDSEMICONDUCTOR LASER, relates to a optically pumped semiconductor laserresonance cavities forming part of a ring resonator, e.g., with a nonlinear crystal located in the ring, including, as discussed, e.g., withrespect to FIGS. 1, 2, 3, 5 & 6, having a bow-tie configuration. U.S.Published Patent Application No. 2004/0202220, published on Oct. 14,2004, with inventors Hua et al, entitled MASTER OSCILLATOR-POWERAMPLIFIER EXCIMER LASER SYSTEM, relates to an excimer laser system,e.g., with in a MOPA configuration, with a set of reflective optics toredirect at least a portion of the oscillator beam transmitted throughthe PA back thru PA ion the opposite direction. U.S. Published PatentApplication No. 2005/0002425, published on Jan. 1, 2003, with inventorsGovorkov et al, entitled MASTER-OSCILLATOR POWER-AMPLIFIER (MOPA)EXCIMER OR MOLECULAR FLUORINE LASER SYSTEM WITH LONG OPTICS LIFETIME,relates to, e.g., a MOPA with a pulse extender and using a beamsplittingprism in the pulse extender, a housing enclosing the (MO+PA) andreflective optics, with the pulse extender mounted thereon, andreflective optics forming a delay line around the PA. U.S. Publishedapplication No. 2006/0007978, published on Jan. 12, 2006, with inventorsGovokov, et al., entitled BANDWIDTH-LIMITED AND LONG PULSE MASTEROSCILLATOR POWER OSCILLATOR LASER SYSTEM, relates to a ring oscillatorwith a prism to restrict bandwidth within the oscillator.

U.S. Pat. No. 6,590,922 issued to Onkels et al. on Jul. 8, 2003,entitled INJECTION SEEDED F2 LASER WITH LINE SELECTION ANDDISCRIMINATION discloses reverse injection of and F₂ laser undesiredradiation centered around one wavelength through a single pass poweramplifier to selectively amplify a desired portion of the F₂ spectrumfor line selection of the desired portion of the F₂ spectrum in amolecular fluorine gas discharge laser. in F2 laser.

U.S. Pat. No. 6,904,073 issued to Yager, et al. on Jun. 7, 2005,entitled HIGH POWER DEEP ULTRAVIOLET LASER WITH LONG LIFE OPTICS,discloses intracavity fluorine containing crystal optics exposed tolasing gas mixtures containing fluorine for protection of the optic.

Published International application WO 97/08792, published on Mar. 6,1997 discloses an amplifier with an intracavity optical system that hasan optical path that passes each pass of a sixteen pass through the sameintersection point at which is directed a pumping source to amplify thelight passing through the intersection point.

R. Paschotta, Regenerative amplifiers, found athttp://www.rp-photonics.com/regenerative_amplifiers.html (2006)discusses the fact that a regenerative amplifier, may be considered tobe an optical amplifier with a laser cavity in which pulses do a certainnumber of round trips, e.g., in order to achieve strong amplification ofshort optical pulses. Multiple passes through the gain medium, e.g., asolid state or gaseous lasing medium may be achieved, e.g., by placingthe gain medium in an optical cavity, together with an optical switch,e.g., an electro-optic modulator and/or a polarizer. The gain medium maybe pumped for some time, so that it accumulates some energy after which,an initial pulse may be injected into the cavity through a port which isopened for a short time (shorter than the round-trip time), e.g., withthe electro-optic (or sometimes acousto-optic) switch. Thereafter thepulse can undergo many (possibly hundreds) of cavity round trips, beingamplified to a high energy level, often referred to as oscillation. Theelectro-optic switch can then be used again to release the pulse fromthe cavity. Alternatively, the number of oscillations may be determinedby using a partially reflective output coupler that reflects someportion, e.g., around 10%-20% of the light generated in the cavity backinto the cavity until the amount of light generated by stimulatedemission in the lasing medium is such that a useful pulse of energypasses through the output coupler during each respective initiation andmaintenance of an excited medium, e.g., in an electrically pumped gasdischarge pulsed laser system, the gas discharge between the electrodescaused by placing a voltage across the electrodes at the desired pulserepetition rate. Uppal et al, Performance of a general asymmetricNd:glass ring laser, Applied Optics, Vol. 25, No. 1 (January 1986)discusses an Nd:glass ring laser. Fork, et al. Amplification offemptosecond optical pulses using a double confocal resonator, OpticalLetters, Vol. 14, No. 19 (October 1989) discloses a seed laser/poweramplifier system with multiple passes through a gain medium in a ringconfiguration, which Fork et al. indicates can be “converted into aclosed regenerative multi pass amplifier by small reorientations of twoof the four mirrors that compose the resonator [and providing]additional means . . . for introducing and extracting the pulse from theclosed regenerator. This reference refers to the open-ended amplifierportion with fixed number of passes through the amplifier portion (fixedby the optics an, e.g., how long it takes for the beam to walk off ofthe lens and exit the amplifier portion as a “resonator”. As used hereinthe term resonator and other related terms, e.g., cavity, oscillation,output coupler are used to refer, specifically to either a masteroscillator or amplifier portion, the power oscillator, as lasing thatoccurs by oscillation within the cavity until sufficient pulse intensityexists for a useful pulse to emerge from the partially reflective outputcoupler as a laser output pulse. This depends on the optical propertiesof the laser cavity, e.g., the size of the cavity and the reflectivityof the output coupler and not simply on the number of reflections thatdirect the seed laser input through the gain medium a fixed number oftimes, e.g., a one pass, two pass, etc. power amplifier, or six or sotimes in the embodiment disclosed in Fork, et al. Mitsubishi publishedJapanese Patent Application Ser. No. JP11-025890, filed on Feb. 3, 1999,published on Aug. 11, 2000, Publication No. 2000223408, entitledSEMICONDUCTOR MANUFACTURING DEVICE, AND MANUFACTURING OF SEMICONDUCTORDEVICE, disclosed a solid state seed laser and an injection locked poweramplifier with a phase delay homogenizer, e.g., a grism or grism-likeoptic between the master oscillator and amplifier. U.S. Publishedapplication 20060171439, published on Aug. 3, 2006, entitled MASTEROSCILLATOR-POWER AMPLIFIER EXCIMER LASER SYSTEM, a divisional of anearlier published application 20040202220, discloses as masteroscillator/power amplifier laser system with an optical delay pathintermediate the master oscillator and power amplifier which createsextended pulses from the input pulses with overlapping daughter pulses.

Partlo et al, Diffuser speckle model: application to multiple movingdiffusers, discusses aspects of speckle reduction. U.S. Pat. No.5,233,460, entitled METHOD AND MEANS FOR REDUCING SPECKLE IN COHERENTLASER PULSES, issued to Partlo et al. on Aug. 3, 1993 discussesmisaligned optical delay paths for coherence busting on the output ofgas discharge laser systems such as excimer laser systems.

The power efficiency of a regenerative amplifier, e.g., using aswitching element, can be severely reduced by the effect of intracavitylosses (particularly in the electro-optic switch). Also, thereflectivity of a partially reflective output coupler can affect bothintracavity losses and the duration of the output pulse, etc. Thesensitivity to such losses can be particularly high in cases with lowgain, because this increases the number of required cavity round tripsto achieve a certain overall amplification factor. A possiblealternative to a regenerative amplifier is a multipass amplifier, suchas those used in applicants' assignee's XLA model laser systemsmentioned above, where multiple passes (with, e.g., a slightly differentpropagation direction on each pass) can be arranged with a set ofmirrors. This approach does not require a fast modulator, but becomescomplicated (and hard to align) if the number of passes through the gainmedium is high.

An output coupler is generally understood in the art to mean a partiallyreflective optic that provides feedback into the oscillation cavity ofthe laser and also passes energy out of the resonance cavity of thelaser.

In regard to the need for improvement of Cost Of Consumables, e.g., forArF excimer lasers, e.g., for photolithography light source use, KrF CoChas long been dominated by chamber lifetime, e.g., due to the robustnessof the optics at the higher 248 nm wavelength for KrF. Recent advancesin Cymer ArF optical components and designs have led to significantincreases in ArF optical lifetimes, e.g., ArF grating life improvementsdeveloped for the Cymer NL-7000A, Low intensity on LNMs, e.g., in twostage XLA systems. ArF etalon material improvements have contributed tolonger life for ArF wavemeters, stabilization modules, LAMs, SAMs, andBAMs. In addition KrF chamber lifetime has been significantly increasedwith Cymer ELS-7000 and ELS-7010 products, e.g., through the use ofproprietary electrode technology. However, longer life electrodetechnology requires specific operating parameters, such as are met inELS-7000 and ELS-7010 KrF chambers, XLA-200 and XLA-300 PA chambers.These parameters, however, are not able to be utilized, e.g., in any ofCymer's ArF XLA MO chambers because of the overall output powerrequirements of the system. Applicants propose ways to alleviate thisdetriment to cost of consumables in, e.g., the ArF dual chamber masteroscillator/amplifier products, used, e.g., for integrated circuitmanufacturing photolithography.

As used herein the term resonator and other related terms, e.g., cavity,oscillation, output coupler are used to refer, specifically to either amaster oscillator or amplifier portion, a power oscillator, as lasingthat occurs by oscillation within the cavity until sufficient pulseintensity exists for a useful pulse to emerge from the partiallyreflective output coupler as a laser output pulse. This depends on theoptical properties of the laser cavity, e.g., the size of the cavity andthe reflectivity of the output coupler and not simply on the number ofreflections that direct the seed laser input through the gain medium afixed number of times, e.g., a one pass, two pass, etc. power amplifier.

SUMMARY OF THE SUBJECT MATTER DISCLOSED

It will be understood by those skilled in the art that an apparatus andmethod is disclosed that may comprise a line narrowed pulsed excimer ormolecular fluorine gas discharge laser system which may comprise a seedlaser oscillator producing an output comprising a laser output lightbeam of pulses which may comprise a first gas discharge excimer ormolecular fluorine laser chamber; a line narrowing module within a firstoscillator cavity; a laser amplification stage containing an amplifyinggain medium in a second gas discharge excimer or molecular fluorinelaser chamber receiving the output of the seed laser oscillator andamplifying the output of the seed laser oscillator to form a lasersystem output comprising a laser output light beam of pulses, which maycomprise a ring power amplification stage. The ring power amplificationstage may comprise an injection mechanism comprising a partiallyreflecting optical element through which the seed laser oscillatoroutput light beam is injected into the ring power amplification stage.The ring power amplification stage may comprise a bow-tie loop or a racetrack loop. The pulse energy of the output of the seed laser oscillatormay be less than or equal to 0.1 mJ, or 0.2 mJ, or 0.5 mJ, or 0.75 mJ.The ring power amplification stage may amplify the output of the seedlaser oscillator cavity to a pulse energy of ≧1 mJ or ≧2 mJ or ≧5 mJ or≧10 mJ or ≧15 mJ. The laser system may operate at an output pulserepetition rate of up to 12 kHz, or ≧2 and ≦8 kHz or ≧4 and ≦6 kHz. Theapparatus and method may comprise a broad band pulsed excimer ormolecular fluorine gas discharge laser system which may comprise a seedlaser oscillator producing an output comprising a laser output lightbeam of pulses which may comprise a first gas discharge excimer ormolecular fluorine laser chamber; a laser amplification stage which maycontain an amplifying gain medium in a second gas discharge excimer ormolecular fluorine laser chamber receiving the output of the seed laseroscillator and amplifying the output of the seed laser oscillator toform a laser system output comprising a laser output light beam ofpulses, which may comprise a ring power amplification stage. Accordingto aspects of an embodiment of the disclosed subject matter a coherencebusting mechanism may be located intermediate the seed laser oscillatorand the amplifier gain medium. The coherence busting mechanism maycomprise an optical delay path having a delay length longer than thecoherence length of a pulse in the seed laser oscillator laser outputlight beam of pulses. The optical delay path may not substantiallyincrease the length of the pulse in the seed laser oscillator laseroutput light beam of pulses. The coherence busting mechanism maycomprise a first optical delay path of a first length and a secondoptical delay path of a second length, with the optical delay in each ofthe first and second delay paths exceeding the coherence length of apulse in the seed laser oscillator laser output light beam of pulses,but not substantially increasing the length of the pulse, and thedifference in the length of the first delay path and the second delaypath exceeding the coherence length of the pulse. The apparatus andmethod according to aspects of an embodiment may comprise a linenarrowed pulsed excimer or molecular fluorine gas discharge laser systemwhich may comprise a seed laser oscillator producing an outputcomprising a laser output light beam of pulses which may comprise afirst gas discharge excimer or molecular fluorine laser chamber; a linenarrowing module within a first oscillator cavity; a laser amplificationstage containing an amplifying gain medium in a second gas dischargeexcimer or molecular fluorine laser chamber receiving the output of theseed laser oscillator and amplifying the output of the seed laseroscillator to form a laser system output comprising a laser output lightbeam of pulses, which may comprise a ring power amplification stage; acoherence busting mechanism intermediate the seed laser oscillator andthe ring power amplification stage. According to aspects of anembodiment the apparatus and method may comprise a broad band pulsedexcimer or molecular fluorine gas discharge laser system which maycomprise a seed laser oscillator producing an output comprising a laseroutput light beam of pulses which may comprise a first gas dischargeexcimer or molecular fluorine laser chamber; a laser amplification stagecontaining an amplifying gain medium in a second gas discharge excimeror molecular fluorine laser chamber receiving the output of the seedlaser oscillator and amplifying the output of the seed laser oscillatorto form a laser system output comprising a laser output light beam ofpulses, which may comprise a ring power amplification stage; a coherencebusting mechanism intermediate the seed laser oscillator and the ringpower amplification stage. The apparatus and method according to aspectsof an embodiment may comprise a pulsed excimer or molecular fluorine gasdischarge laser system which may comprise a seed laser oscillatorproducing an output comprising a laser output light beam of pulses whichmay comprise a first gas discharge excimer or molecular fluorine laserchamber; a line narrowing module within a first oscillator cavity; alaser amplification stage containing an amplifying gain medium in asecond gas discharge excimer or molecular fluorine laser chamberreceiving the output of the seed laser oscillator and amplifying theoutput of the seed laser oscillator to form a laser system outputcomprising a laser output light beam of pulses; a coherence bustingmechanism intermediate the seed laser oscillator and the laseramplification stage comprising an optical delay path exceeding thecoherence length of the seed laser output light beam pulses. Theamplification stage may comprise a laser oscillation cavity or anoptical path defining a fixed number of passes through the amplifyinggain medium. The coherence busting mechanism may comprise comprising acoherence busting optical delay structure generating multiple sub-pulsesdelayed sequentially from a single input pulse, wherein each sub-pulseis delayed from the following sub-pulse by more than the coherencelength of the pulse light.

It will also be understood by those skilled in the art that an apparatusand method is disclosed that may comprise a processing machine which maycomprise an irradiation mechanism irradiating a workpiece with pulsed UVlight; a UV light input opening; a workpiece holding platform; acoherence busting mechanism comprising an optical delay path exceedingthe coherence length of the UV light pulses. The optical delay path maynot substantially increase the length of the UV light pulse. Thecoherence busting mechanism may comprise a first optical delay path of afirst length and a second optical delay path of a second length, withthe optical delay in each of the first and second delay paths exceedingthe coherence length of the UV light pulse, but not substantiallyincreasing the length of the pulse, and the difference in the length ofthe first delay path and the second delay path exceeding the coherencelength of the pulse. At least one of the first and second optical delaypaths may comprise a beam flipping or beam translating mechanism.

It will also be understood by those skilled in the art that an apparatusand method is disclosed which may comprise according to aspects of anembodiment a laser light source system which may comprise a solid statelaser seed beam source providing a seed laser output; a frequencyconversion stage converting the seed laser output to a wavelengthsuitable for seeding an excimer or molecular fluorine gas dischargelaser; an excimer or molecular fluorine gas discharge laser gain mediumamplifying the converted seed laser output to produce a gas dischargelaser output beam of pulses at approximately the converted wavelength; acoherence busting mechanism comprising an optical delay element having adelay path longer than the coherence length of the output pulse. Theexcimer or molecular fluorine laser may be selected from a groupcomprising XeCl, XeF, KrF, ArF and F₂ laser systems. The laser gainmedium may comprise a power amplifier, which may comprise a single passamplifier stage or a multiple-pass amplifier stage. The gain medium maycomprise a ring power amplification stage, which may comprise a bow-tieconfiguration or race track configuration and may also comprise aninput/output coupler seed inject mechanism. The coherence bustingmechanism may be intermediate the laser seed beam source and the gasdischarge laser gain medium. The solid state seed laser beam source maycomprise an Nd-based solid state laser and may comprise a frequencydoubled pump pumping the Nd-based solid state laser. The Nd-based solidstate laser may comprise a fiber amplifier laser and may comprise anNd-based solid state laser selected from a group which may compriseNd:YAG, Nd:YLF and Nd:YVO₄ solid state lasers. The solid state seedlaser beam source may comprise an Er-based solid state laser, which maycomprise a fiber laser. The Er-based solid state laser may comprise anEr:YAG laser. The frequency conversion stage may comprise a linearfrequency converter, which may comprise a Ti:Sapphire crystal or acrystal comprising Alexandrite. The frequency conversion stage maycomprise a non-linear frequency converter, e.g., a second harmonicgenerator or a sum-frequency mixer. The apparatus and method accordingto aspects of an embodiment may comprise a laser light source systemwhich may comprise a solid state laser seed beam source providing a seedlaser output; frequency conversion stage converting the seed laseroutput to a wavelength suitable for seeding an excimer or molecularfluorine gas discharge laser; an excimer or molecular fluorine gasdischarge laser gain medium amplifying the converted seed laser outputto produce a gas discharge laser output at approximately the convertedwavelength, which may comprise a ring power amplification stage. Themethod may comprise utilizing a solid state laser seed beam source toprovide a seed laser output; frequency converting in a frequencyconversion stage the seed laser output to a wavelength suitable forseeding an excimer or molecular fluorine gas discharge laser; utilizingan excimer or molecular fluorine gas discharge laser gain medium,amplifying the converted seed laser output to produce a gas dischargelaser output at approximately the converted wavelength.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows as known MOPA configured multi-chamber laser system;

FIG. 2 shows aspects of an embodiment of the claimed subject matterdisclosed;

FIG. 3 shows aspects of an embodiment of the claimed subject matterdisclosed;

FIG. 4 shows aspects of an embodiment of the claimed subject matterdisclosed;

FIG. 5 shows aspects of an embodiment of the claimed subject matterdisclosed;

FIG. 6 shows aspects of an embodiment of the claimed subject matterdisclosed;

FIG. 7 illustrates a timing and control regime according to aspects ofan embodiment of the subject matter disclosed;

FIG. 8 illustrates schematically multiple reflections similar to thoseof FIG. 37, or the use of separate beams to fill different spatialportions of an aperture according to aspects of an embodiment of thesubject matter disclosed;

FIG. 9 illustrates schematically input coupling useful according toaspects of an embodiment of the subject matter disclosed;

FIG. 10 illustrates schematically input coupling useful according toaspects of an embodiment of the subject matter disclosed;

FIG. 11 illustrates schematically input coupling useful according toaspects of an embodiment of the subject matter disclosed;

FIG. 12 illustrates schematically input coupling useful according toaspects of an embodiment of the subject matter disclosed;

FIG. 13 illustrates schematically input coupling useful according toaspects of an embodiment of the subject matter disclosed;

FIG. 14 illustrates schematically input coupling useful according toaspects of an embodiment of the subject matter disclosed;

FIG. 15 illustrates schematically a top view of aspects of an embodimentof an input coupling mechanism useful according to aspects of anembodiment of the subject matter disclosed;

FIG. 16 illustrates schematically a side view of the input couplingmechanism of FIG. 15 useful according to aspects of an embodiment of thesubject matter disclosed;

FIG. 17 illustrates schematically input coupling useful according toaspects of an embodiment of the subject matter disclosed;

FIG. 18 illustrates schematically illustrates in cross section aspectsof an embodiment of an orthogonal injection seeding mechanism accordingto aspects of an embodiment of the subject matter disclosed;

FIG. 19 illustrates schematically illustrates in cross section aspectsof an embodiment of an orthogonal injection seeding mechanism accordingto aspects of an embodiment of the subject matter disclosed;

FIG. 20 illustrates schematically illustrates in cross section aspectsof an embodiment of a beam returner according to aspects of anembodiment of the subject matter disclosed;

FIG. 21 illustrates schematically illustrates in cross section aspectsof an embodiment of a beam returner according to aspects of anembodiment of the subject matter disclosed;

FIG. 22 illustrates schematically illustrates in cross section aspectsof an embodiment of a beam returner according to aspects of anembodiment of the subject matter disclosed;

FIG. 23 illustrates partly schematically in a partially cut awayperspective view an extension of a lasing chamber containing opticalelements in the chamber according to aspects of an embodiment of thesubject matter disclosed;

FIG. 24 illustrates measurements of forward and backward energy in aring power amplifier according to aspects of an embodiment of thesubject matter disclosed;

FIG. 25 illustrates measurements of forward and backward energy in aring power amplifier according to aspects of an embodiment of thesubject matter disclosed;

FIG. 26 illustrates schematically and in block diagram form a timing andcontrol system for a MOPO according to aspects of an embodiment of thesubject matter disclosed;

FIG. 27 illustrates the degree of saturation of a ring power oscillatorwith variation of MO output pulse energy according to aspects of anembodiment of the subject matter disclosed;

FIG. 28 shows schematically and in block diagram form a laser controlsystem according to aspects of an embodiment of the subject matterdisclosed;

FIG. 29 shows schematically and in block diagram form a laser controlsystem according to aspects of an embodiment of the subject matterdisclosed;

FIG. 30 shows schematically a seed injection mechanism and beam expanderaccording to aspects of an embodiment of the subject matter disclosed;

FIG. 31 shows schematically a coherency buster according to aspects ofan embodiment of the disclosed subject matter;

FIG. 32 shows schematically a coherence buster according to aspects ofam embodiment of the disclosed subject matter;

FIG. 33 shows partly schematically and partly in block diagram for anexample of elements of a coherence busting scheme and the results ofaspects of the scheme according to aspects of an embodiment of thedisclosed subject matter;

FIG. 34 illustrates relative speckle intensity for a various E-Odeflector voltages related to relative timing between the E-O and thepulse generation in the seed laser according to aspects of an embodimentof the disclosed subject matter;

FIG. 35 illustrates pointing shift relative to E-O voltage according toaspects of an embodiment of the disclosed subject matter;

FIG. 36 illustrates an example of the timing of an E-O deflectionvoltage and a seed laser pulse spectrum according to aspects of anembodiment of the disclosed subject matter;

FIG. 37 illustrates schematically the effect on beam coherency fromfolding a beam upon itself according to aspects of an embodiment of thedisclosed subject matter;

FIG. 38 illustrates the effect of beam sweeping/painting on coherencyaccording to aspects of an embodiment of the disclosed subject matter;

FIG. 39 shows schematically and in cartoon fashion the effects ofmultiple coherence busting schemes;

FIG. 40 illustrates schematically a coherency reduction scheme accordingto aspects of an embodiment of the disclosed subject matter;

FIG. 41 illustrates results of simulated beam pulse flipping results;

FIG. 42 illustrates schematically and in partly block diagram form abeam combiner with divergence control according to aspects of anembodiment of the disclosed subject matter;

FIG. 43 illustrates a simulated E-O supply voltage with respect to aseed pulse intensity spectrum over time, according to aspects of anembodiment of the disclosed subject matter;

FIG. 44 illustrates a test E-O supply voltage with respect to a seedpulse intensity spectrum over time, according to aspects of anembodiment of the disclosed subject matter;

FIG. 45 illustrates a E-O cell drive circuit according to aspects of anembodiment of the disclosed subject matter;

FIG. 46 illustrates exemplary test results according to aspects of anembodiment of the disclosed subject matter;

FIG. 47 illustrates schematically and in block diagram form a broad bandlight source and laser surface treatment system using the DUV laserlight according to aspects of an embodiment of the disclosed subjectmatter;

FIG. 48 shows schematically a coherence buster optical delay pathaccording to aspects of an embodiment of the disclosed subject matter;

FIG. 49 shows schematically a coherence buster optical delay pathaccording to aspects of an embodiment of the disclosed subject matter.

FIG. 50 shows schematically and in block diagram form a photolithographytool according to aspects of an embodiment of the subject matterdisclosed;

FIG. 51 shows schematically and in block diagram form a photolithographytool according to aspects of an embodiment of the subject matterdisclosed;

FIG. 52 shows schematically and in block diagram form a laserphotolithography tool according to aspects of an embodiment of thesubject matter disclosed;

FIG. 53 shows schematically and in block diagram form a laserphotolithography tool according to aspects of an embodiment of thesubject matter disclosed;

FIG. 54 shows schematically and in block diagram form a very highaverage power laser light source according to aspects of an embodimentof the disclosed subject matter;

FIG. 55 illustrates schematically and in block diagram form a very highaverage power laser light source according to aspects of an embodimentof the disclosed subject matter;

FIG. 56 shows schematically in block diagram form an example of a veryhigh average power laser light source according to aspects of anembodiment of the disclosed subject matter;

FIG. 57 shows partly schematically and partly in block diagram form, byway of example an immersion laser lithography system according toaspects of an embodiment of the disclosed subject matter;

FIG. 58 shows schematically and in block diagram form a solid state seedlaser to gas discharge amplifier laser system according to aspects of anembodiment of the disclosed subject matter;

FIG. 59 shows in block diagram form a solid state seed laser/amplifierlaser system according to aspects of an embodiment of the disclosedsubject matter;

FIG. 60 shows schematically and in block diagram form conversion of theoutput of a seed laser, e.g., with a frequency converter along with abeam divider, followed by coherency busting according to aspects of anembodiment of the disclosed subject matter;

FIG. 61 shows schematically and in block diagram form a version of theembodiment of FIG. 60 according to aspects of an embodiment of thedisclosed subject matter;

FIG. 62 shows schematically and partly in block diagram form aninjection seeded DUV gas discharge master oscillator/amplifier gainmedium laser system solid state master oscillator according to aspectsof an embodiment of the disclosed subject matter;

FIG. 63 shows schematically and partly in block diagram form aninjection seeded DUV gas discharge master oscillator/amplifier gainmedium laser system solid state master oscillator according to aspectsof an embodiment of the disclosed subject matter;

FIG. 64 shows schematically and partly in block diagram form aninjection seeded DUV gas discharge master oscillator/amplifier gainmedium laser system solid state master oscillator according to aspectsof an embodiment of the disclosed subject matter;

FIG. 65 shows schematically and partly in block diagram form aninjection seeded DUV gas discharge master oscillator/amplifier gainmedium laser system solid state master oscillator according to aspectsof an embodiment of the disclosed subject matter;

FIG. 66 illustrates schematically and in partly block diagram form avery high power solid state seed laser and gain amplifier laser systemaccording to aspects of an embodiment of the disclosed subject matter;

FIG. 67 illustrates schematically and partly in block diagram format aregenerative/recirculating power gain oscillator power amplificationstage according to aspects of an embodiment of the disclosed subjectmatter;

FIG. 68 illustrates schematically and partly in block diagram form asolid state seed laser/gain amplifier laser system according to aspectsof an embodiment of the disclosed subject matter;

FIG. 69 illustrates schematically and partly in block diagram form asolid state seed laser/gain amplifier laser system according to aspectsof an embodiment of the disclosed subject matter;

FIG. 70 illustrates normalized output pulse shapes from laser systemsaccording to aspects of an embodiment of the disclosed subject matter;

FIG. 71 represents schematically E-O cell laser steering input voltagesaccording to aspects of an embodiment of the disclosed subject matter;

FIG. 72 represents schematically in block diagram form a laser steeringsystem according to aspects of an embodiment of the disclosed subjectmatter;

FIG. 73 represents schematically E-O cell laser steering voltages inputsignals according to aspects of an embodiment of the disclosed subjectmatter;

FIG. 74 illustrates exemplary coherency busting test results accordingto aspects of an embodiment of the disclosed subject matter;

FIG. 75 illustrates exemplary coherency busting test results accordingto aspects of an embodiment of the disclosed subject matter;

FIG. 76 illustrates schematically and partly in block diagram form asolid state seed laser with about 193 nm output light according toaspects of an embodiment of the disclosed subject matter;

FIG. 77 illustrates schematically and partly in block diagram form asold state seed laser with about 193 nm output light according toaspects of an embodiment of the disclosed subject matter;

FIG. 78 illustrates various frequency up-conversion schemes;

FIG. 79 shows schematically and in block diagram form a laser systemaccording to aspects of an embodiment of the disclosed subject matter;

FIG. 80 shows schematically and in block diagram form a laser systemaccording to aspects of an embodiment of the disclosed subject matter;

FIGS. 81 A-C illustrate in exploded form a perspective and partlyschematic view of a ray path for a seed laser amplification gain mediumaccording to aspects of an embodiment of the disclosed subject matter;

FIGS. 82 A and B illustrate a perspective view partly schematic of a topand side view of a portion of the ray path of FIGS. 81 A-C;

FIG. 83A illustrates a perspective partly schematic view of a portion ofthe relay optics of FIGS. 81 A-C and 82 A-B;

FIG. 83 B illustrates a side view in more detail of the beam expander ofFIGS. 81 A-C, 82 A-B, and 83 A;

FIGS. 84A and B illustrate schematically a top view and side view of abeam spatial translation/fan out/chirp mechanism according to aspects ofan embodiment of the disclosed subject matter;

FIG. 85 is a chart of beam displacement to offset angle; and,

FIG. 86 illustrates schematically a bean flipping mechanism within abeam delay path according to aspects of an embodiment of the disclosedsubject matter.

DETAILED DESCRIPTION

According to aspects of an embodiment of the subject matter disclosed again amplification medium suitable for use with, e.g., an excimer ormolecular fluorine gas discharge seed oscillator laser in amulti-chamber (multi-portion) oscillator/amplifier configuration, thiscould be, e.g., a master oscillator power gain amplificationconfiguration, which may take advantage of improved seed laser couplingarrangements, fundamentally designed to insert seed laser light, e.g.,master oscillator seed output laser light pulse beam pulses, into anamplifying gain medium, generally with little loss and with protectionagainst amplifier oscillation and/or ASE returning to the masteroscillator while the master oscillator laser medium is excited. Suchcould interfere with the proper operation of the master oscillator,e.g., in conjunction with the line narrowing module producing theappropriately narrowed seed oscillator output laser light pulse beampulse bandwidth.

According to aspects of an embodiment of the subject matter disclosed,however, a preferred configuration may comprise, e.g., a ring cavity,e.g., a power oscillator or Power Ring Oscillator (“PRO”) or a PowerRing Amplifier (“PRA”). Such a configuration has been determined byapplicants to be a very effective solution to going to higher powerlaser operation in a line narrowed multi-portion (seed laser-amplifier)arrangement, particularly for gas discharge seed laser to identical gasdischarge amplifier laser multi-portion laser systems. Such a lasersystem could be similar in operation to applicants' employers' XLAseries lasers, though with a power ring amplification stage. Improvementin CoC may be attained according to a aspects of an embodiment of thesubject matter disclosed.

Also, however, a power ring amplification stage may be useful for otherapplications, including with seed lasers of other than the same type ofgas discharge laser, e.g., a solid state seed, e.g., matched to thelasing wavelength of an excimer or molecular fluorine amplifier, e.g.,by frequency shifting and/or frequency multiplication. Such systems maybe useful for ultimate control of laser system output laser light pulsebeam pulse parameters, e.g., bandwidth, bandwidth stability, outputpulse energy, output pulse energy stability and the like. In suchsystems pulse trimming, e.g., at the output of the amplification stagemay also be useful for control of laser system output pulse parameters.Thus, according to aspects of an embodiment of the subject matterdisclosed a ring cavity PO may be constructed, e.g., with a 24% outputcoupler, e.g., comprising an existing OPuS beamsplitter, as explainedmore fully below.

According to aspects of an embodiment of the subject matter disclosedapplicants propose to re-arrange, e.g., an existing XLA product, e.g.,with an excimer-based MO, from a MOPA to a MOPRO (power ringoscillator), or to a MOPRA, a seed laser with a regenerative amplifier,e.g., in a ring configuration (a power regenerative amplifier),collectively refereed to herein sometimes as a power amplificationstage, in accordance with aspects of an embodiment of the subject matterdisclosed. Such a system can (1) improve energy stability, e.g., byoperating the amplification stage at saturation, or effectivelysaturation, pulse to pulse, thereby more accurately insuring pulse topulse energy stability, (2) achieve longer LNM life.

The advantages of the multi-chambered laser system according to aspectsof an embodiment of the subject matter disclosed enable meeting theabove discussed requirements for, e.g., higher power, better pulseenergy stability, better bandwidth control and lower achievablebandwidth, higher repetition rates and lower cost of operation. Further,increases in currently available laser system output light average powermay be attained. This may be beneficial both for line narrowed systemsand for broad band systems, e.g., XeCl or XeF multi-chamber lasersystems used, e.g., for annealing amorphous silicon on substrates, e.g.,in LTPS processes, e.g., for the manufacture of crystallized substratesfor the production of, e.g., thin film transistors.

According to aspects of an embodiment of the disclosed subject matterthere are certain performance requirements desirous of a very high poweramplification stage cavity for, e.g., a 120-180 W or higher lasersystem, e.g., with two amplifier gain medium chambers in parallel.Examples noted herein may be based upon a presumption that therequirement may be 200 W or higher. They should produce linearpolarization (>98%). Each amplification stage should produce, andsurvive, ≧40 W average output energy, e.g., at 193 nm wavelength of ArF,although an expectation of ≧60 w may also be the specification, or lessstringently at longer wavelengths, e.g., 248 for KrF and 351 for XeF or318 for XeCl, though even more stringent for F₂ at 157 nm. Eachamplification stage in one embodiment may operate at least about 4 kHzor above, with 6 kHz or above also being an expectation in some cases.According to aspects of an embodiment of the disclosed subject matter,the amplification stage(s) can exhibit full seeding (at or nearsaturation) with relatively small seed laser energy. Applicants believethat the amplification stage may also need to support a moderately largeangular distribution for some applications, e.g., to maintain the sameangular spread of the seed laser, in order to avoid inadvertentlyimproving coherence by, e.g., removing coherence cells, e.g., with arange of angles of within a few m Rad. Protection of the seed laser fromreverse traveling radiation is also an important operationalrequirement. When properly seeded, ASE levels produced by theamplification stage, according to aspects of an embodiment of thedisclosed subject matter, should be less than 0.1% or less of the totaloutput.

According to aspects of an embodiment of the disclosed subject matterapplicants expect that (1) the gain cross-section will be similar toexisting ArF chambers, e.g., applicants' assignee's XLA ArF laser systempower amplifier (“PA”) chambers, (2) the gain length will also besimilar to existing ArF chambers, (3) the gain duration will also besimilar to existing ArF chambers.

According to aspects of an embodiment of the disclosed subject matter,applicants propose, e.g., a single MO/gain amplification medium XLAtic-toc with a solid state seed laser operating at 12 kHz with about a 1mJ seed laser output light pulse energy and the two amplification stageseach operating at around a 17 mJ output pulse energy, i.e., alternatelyamplifying in respective amplification gain medium chambers tic and tocoutput pulses from the seed laser divided to alternately enter in serialform the respective two amplification gain mediums (which could alsoinclude, as explained herein) more than two amplification gain mediumsand pulses divided into more than in alternate pulses, e.g., three gainmediums and three pulses divided out seriatim from the seed pulse outputfor respective gain mediums, repeated over time, so the gain mediums runat a pulse repetition rate that is a fraction of that of the seed laser,depending upon the number of gain mediums used in parallel on the seedlaser output.

In addition, according to aspects of an embodiment of the disclosedsubject matter, applicants propose the utilization of a regenerativegain medium in which the oscillating laser generated light photons passthrough the gain medium, e.g.; a ring power amplification stage, a ringpower oscillator or a ring power amplifier, which can be more efficientat amplification of the seed pulse energy from the seed laser ascompared, e.g., to a power amplifier amplification stage in (“PA”) in aMOPA configuration, with an optically defined fixed number of passesthrough the gain medium. For testing purposes applicants have simulatedthe input from a solid state 193 nm seed laser using a line-narrowed ArFlaser.

Applicants have studied ASE vs. MO-PO timing difference for thedifferent values of the above noted parameters with results as indicatedin FIG. 75. Similarly a study of MOPO energy vs. MO-PO timing as afunction of these same parameters also illustrated in FIG. 75.

In order to meet the requirements noted above, including, e.g., theconstraints of known lithography laser light source technology,applicants propose, according to aspects of an embodiment of thedisclosed subject matter, a number of overall architectures that arebelieved to provide workable ways to address the requirements andconstraints noted above. The first may be to provide two multi-chamberlaser systems along the lines of applicants' assignee's XLA XXX lasersystem series, e.g., with two dual chamber laser oscillator/poweramplifier arrangements whereby each is configured to run at around above4 kHz and preferably around 6 kHz, producing output pulses at about 17mJ with interleaved firing times to produce, according to an embodiment,a single approximately 12 kHz system producing about 17 m per pulse.

Turning now to FIG. 1 there is shown schematically and partly in blockdiagram form a more or less typical MOPA laser system 20, such asapplicants' assignees XLA multi-chamber MOPA laser systems. The lasersystem 20 may include, e.g., an oscillator seed laser chamber 22, and anamplifier gain medium laser chamber 24, e.g., a multi-pass poweramplifier (“PA”). The MO 22 may have associated with it, e.g., forapplications such as semiconductor manufacturing photolithography, aline narrowing module (“LNM”) 26, or if desired to be operated inbroadband mode, e.g., for application such as LTPS, it may not have linenarrowing. An output coupler 28, e.g., a partially reflective mirror,e.g., with a selected reflectivity for the applicable nominal centerwavelength, e.g., about 351 for XeF laser oscillators, 248 nm for KrFlaser oscillators, 193 nm for ArF laser oscillators and 157 formolecular fluorine laser oscillators, along with the rear end reflectionprovided by the LNM 26 (or a maximally reflective mirror for the givennominal center wavelength, not shown, substituted for the LNM 26 in thecase of broad band operation), may serve to form the laser 20 oscillatorcavity.

Relay optics 40, e.g., including a turning mirror 44 and a turningmirror 46, may serve to steer the seed oscillation laser 20 output laserlight pulse beam 62 pulses exiting a line center (center wavelength)analysis module (“LAM”) 42 along a light path (optical axis) 60 to theinput of the amplifier module lasing chamber 24. The LAM, in addition tocenter wavelength monitoring equipment (not shown) may include an MOenergy monitor 48, which may be provided with a small portion of thelaser output light pulse beam from the MO chamber 22 for metrologypurposes, e.g., for nominal center wavelength and energy detection, by abeam splitter 50 inside the LAM 42. The turning mirror 44 may providethe master oscillator 22 output laser light pulse beam 62 pulses to theturning mirror 46 along an optical path beam path, which may reflect thebeam 62 into the amplifier chamber 24 as a beam 64.

In the case of the system 20 of FIG. 1 the gain amplifier 24 is set upas a power amplifier, i.e., the light received from the MO, the MO seedoutput laser light pulse beam pulses passes through the gainamplification medium a fixed number of times, e.g., determined by theoptics, including the turning mirror 46, set up as illustratedschematically in FIG. 1 as an edge coupling optic and a beam returner(reverser) optic 70, e.g., a retro-reflecting mirror, discussed in moredetail below, along a beam path 72, exiting the laser gain mediumthrough a window 80, which may be, e.g., set at an angle, e.g., around70° to the exiting beam path 72 in order to optimize energy densityreduction on optical elements and thus the thermal loading for the givennominal center wavelength and the material of the window 80, e.g., CaF₂for shorter wavelengths such as the nominal center wavelength for an ArFlaser system, or at around Brewster's angle to optimize thetransmissivity of the exiting light. The exit light 100 may also passthrough a beam splitter 75 within a bandwidth analysis module (“BAM”)82. The laser system output beam 100 may also pass through a first beamsplitter 76 and a second beam splitter 78 within a pulse stretcher 86,e.g., an Optical Pulse Stretcher (“OPuS”), such as are included withmany of applicants' assignees' laser systems discussed above as a 4×pulse stretcher, e.g., increasing the T_(is) of the laser system 20output laser light pulse beam 100 pulses exiting the system as beam 100from about 17 ns to about 40 ns, by directing the beam 100 into delaypath 88, as is more fully described in, e.g., U.S. Pat. No. 6,928,093,entitled LONG DELAY AND HIGH TIS PULSE STRETCHER, issued to Webb et al.on Aug. 9, 2005 referenced above.

Also in the path of the laser system 20 output laser light pulse beam100 pulses may be, e.g., a beam expander 84, e.g., to decrease theenergy density on downstream optics, including the OPuS 86 beamsplitters 76, 78 and optical delay ling mirrors 90 and optics, e.g., inthe scanner (not shown) utilizing the laser system 20 output laser lightpulse beam 100 pulses. The laser system 20 may also include a shutter96, including, e.g., a shutter beam splitter 98, e.g., taking off aportion of the laser system 20 output laser light pulse beam 100 pulsesfor energy measurement in an output energy monitor (not shown) in theshutter 96.

OPuS 86

This existing XLA MOPA configuration, shown in FIG. 1 is illustratedschematically further in the sense that the illustration switchesbetween the horizontal and vertical axis in several places in order tomake this schematic illustration simpler and easier to understand. Noneof the concepts described here are impacted by properly drawing thehorizontal and vertical axis of the light paths.

Turning to FIG. 2 there is illustrated a conversion from a MOPAconfiguration to a master oscillator along with a power oscillationamplification or a regenerative amplification configuration poweramplification stage according to aspects of an embodiment of the subjectmatter disclosed, e.g., including a power ring amplification stage,e.g., with a ring cavity power oscillator (also known as a ring cavityregenerative amplifier) formed between the beam reverser 70 and thelower turning mirror 44, replaced with, e.g., an injection seedingmechanism 160 according to aspects of an embodiment of the subjectmatter disclosed. The BAM 82 as shown in FIG. 1 may be moved or itsfunctionality included within the shutter 96.

According to aspects of an embodiment of the subject matter disclosedmay include, e.g., placing the a beam expander 142 comprising, e.g.,first and second beam expanding and dispersing prisms 146, 148 inside ofan entrance window and beam expander housing 140 which may be affixed tothe gain medium chamber 144 by a suitable means, e.g., welding orbolting with suitable sealing mechanisms. These optics 146, 148 may beplaced inside the ring cavity formed between the orthogonal seedinjection mechanism 160 input/output coupling partially reflectingmirror 162 and the beam returner 70, e.g., in order to reduce the energydensity on the maximum reflector forming the beam returner 70, e.g., asillustrated in FIGS. 20-22, which may be composed of, e.g., CaF₂, e.g.,a beam splitter of the type currently used in applicants' assignee'sOPuSs, and coated with a coating that, e.g., reflects 20% of theincident light, that makes up a portion 162 of the seed injectionmechanism 160 of the ring power amplification stage cavity discussed inmore detail below. The prisms may be non-dispersive in embodiments wherethe power amplification stage is configured not to oscillate on its own,thus removing the need to lessen or remove ASE from the system output.The beam reverser 70 may also be moved to inside the cavity gain mediumcavity chamber 144 with the attachment of a housing 150 similar to thatof housing 140.

The beam expander optics 146, 148 and beam returner/reverser 70, due totheir makeup including a fluorine containing crystal and their exposureto fluorine in the lasing medium gas in the chamber 144 and housings140, 150 may be protected from optical damage. The AMPLIFICATION STAGEchamber window 168 similarly constructed, e.g., of a fluorine containingcrystal, e.g., CaF₂, need not have a protective coating on its faceexposed to the highest energy density, facing the ring power oscillatoroscillation cavity, due in part to its beam expansion in the beamexpanded 14Z in the cavity and also to using around a 45° angle, e.g., a47 degree orientation.

According to aspects of an embodiment of the subject matter disclosed aring power oscillator cavity, e.g., as illustrated by way of example inFIG. 2, e.g., with beam expansion on the output coupler side of thechamber 144 and with the beam expansion prisms 146, 148 oriented toproduce a net dispersion (where useful for ASE reduction orelimination), has a number of notable advantages, including, e.g.,making very efficient use of seed energy, eliminating the need forprotective coatings for high power and very short nominal centerwavelength, especially at 193 nm and below, dispersion in the cavity,which can, e.g., help to decrease the ASE ratio, and acceptable energydensity on the optics, e.g., forming the output coupler portion 162 ofthe ) seed injection mechanism and the maximally reflective mirror(“Rmax”) portion 164 of the seed injection mechanism, which may or maynot be coated as needed, e.g., as is done in applicants' assignee'sOPuSs on existing laser systems (beam splitters 76, 78 and mirrors 90).In addition, the arrangement can, e.g., perform the needed beamexpansion function prior to the laser system output laser light pulsebeam 100 entering the OPuS 86, and the chamber 144 with additions 140and 150 can easily be created from applicant's assignee's existingchambers, e.g., XLA model chambers, e.g., by adding two “snouts” 140,150, e.g., in place of existing window mounting assemblies. This isshown, e.g., in more detail partially schematically FIG. in 23.

Further, all optics inside the chamber, e.g., including the snouts 140,150 can be, e.g., further removed from the source of chamber dust. Theconfiguration can also be made to fit, e.g., within a present XLA opticsbay.

As explained elsewhere, the ring cavity, e.g., as shown in FIGS. 12 and13, may also be used with a relatively long round trip time, e.g., about7 ns to traverse, e.g., from the input/output coupler beam splitter 262to the beam reverser 270 and back to the beam splitter 262. Also, ofcourse, especially in broad band embodiments, but also in line narrowedembodiments, according to aspects of an embodiment of the subject matterdisclosed using the more typical 1-3 mJ MO output greatly increases theaverage power out of the amplification stage over that of, e.g., currentXLA-XXX laser systems.

Low MO chamber pressure has a number of longer chamber life benefits.

Rather than having to contemplate ways to simply survive high raw power,e.g., in the 200 W range, applicants, according to aspects of anembodiment of the subject matter disclosed contemplate being able toinstead focus on bettering energy stability, pointing stability, profilestability, and ASE stability of contemplated configuration while,operating at full repetition rate, e.g., between 4 kHz and 6 kHz andeven above.

Turning now to FIG. 3 there is shown illustratively and partlyschematically and in block diagram form a ring power amplification stagelaser system 400, which in addition to the elements shown in FIG. 2 mayinclude, e.g., an injection seeding coupler mechanism 160 that isaligned with a chamber input/output window 94 and with beam expansionand dispersion optic 170, e.g., comprising beam expanding and dispersingprisms 172 and 174, which can e.g., contract and steer and disperse thebeam 64 to one path 74 to the beam reverser 70 in chamber extension 150and back to the input/output coupler partially reflective mirror 162.Baffles 190 and 192, respectively may protect the optics in the rearsnout 150 and the front snout 140, form, e.g., dust circulating withinthe chamber 144.

In FIG. 4 a similar system 410, according to aspects of an embodiment ofthe subject matter disclosed, may include, e.g., the beamreturner/reverser 170 outside of the chamber 14A, which may incorporatemodified snouts 140, 150, e.g., to protect, respectively, frontinput/output window 194 and rear window 196 from circulating dust, alongwith baffles 190, 192. This embodiment may include, e.g., Brewsterwedges 420 and 430, for the purpose of, e.g., clearing the desirablepolarization by reflecting the undesirable polarization out of theoptical cavity.

FIG. 5 illustrates schematically and partly in block diagram format asystem 330 in which, e.g., a ring power amplification stage is set upby, e.g., the use of a polarizing beam splitter 336, half wave plate 338and output coupler 340. In operation the seed laser 334 feeds a seedlaser output laser light pulse beam 62 to the beam splitter 336 and thering cavity is set up with a single maximally reflective rear mirror342, e.g., and a partially reflective output couple 340.

Similarly a ring cavity may be set up according to aspects of anembodiment of the subject matter disclosed as illustrated in FIG. 6between an output coupler 410 and a rear cavity mirror 412.

There are a number of possible ways to couple the output laser lightpulse beam pulses from the MO to the power amplification stage, e.g., asillustrated schematically and partly in block diagram format in FIGS.9-11 and 14. As shown in FIG. 9, e.g., a partial reflection inputcoupled oscillator amplification stage or power regenerative amplifier200 may have a chamber 202 and, e.g., a partial reflective optic 204 asan input coupler to the oscillator chamber, with a front partiallyreflective optic output coupler 206. In operation, the MO output 62enters the cavity, 200, shown to be a normal oscillator, rather than aring oscillator, for purposes of, e.g., clarity of description, andoscillates within the cavity formed by the entrance partially reflectingoptic 204 and the output coupler partially reflective optic 206, untiloscillation results in a significant enough pulse of laser system outputlight pulse beam 100 leaving the output coupler as is well understood inthe art.

Illustrated schematically and partly in block diagram form in FIG. 10, apolarization input coupled oscillator 220 forming the ring poweramplification stage may include, e.g., a chamber 210, a polarizing beamsplitter 212, a quarter wave plate 214, a rear maximally reflectivemirror and an output coupler 216. In operation, the maximally reflectivemirror 218 and the output coupler 216 for an oscillator cavity like thatof FIG. 2, also shown as a regular oscillator, rather than a ringoscillator, for convenience. The polarizing beam splitter and quarterwave plate 214 serve, e.g., to isolate the MO from the amplificationstage. The incoming beam 62 is of a polarity that is reflected by thebeam splitter 212 into the cavity, with, e.g., the quarter wave plate214 transmitting the beam 62 into the cavity as circularly polarized andconverting the return beam from the output coupler 216 to a polarizationtransmitted by the polarizing beam splitter 212.

As illustrated in FIG. 11 a switched input/output coupler coupledoscillator 230 is shown schematically and partly in block diagram formatin which, e.g., a chamber 232 may be contained within a cavity formed,e.g., by a maximally reflective mirror 240 and a window 238, with, e.g.,an electro-optic switch, e.g., a Q-switch 236, acting as a switch toallow oscillation to build to a selected point and then the Q switch isactivated to allow a laser system output laser pulse beam 100 pulse tobe emitted.

Illustrated in FIG. 12 schematically and in partial block diagram formis a multi-pass regenerative ring oscillator laser system 250, accordingto aspects of an embodiment of the subject matter disclosed, which mayinclude, e.g., an amplifier chamber 252 and a seed laser 254 the system250 may also include an input/output coupler, e.g., an injection seedinput/output coupler mechanism 260. The input/output coupler 260 mayinclude, e.g., a partially reflective mirror 262, which may be, e.g., abeam splitter of the type used currently by applicants' assignee's OPuSssold with its laser equipment. The system 250 may also include, e.g., amaximally reflective optic 264, to steer the MO beam 62 into theelectrode region of the cavity as one pass beam 276 which may return tothe output coupler 262 as a second pass beam 278 from a beamreverser/returner 270, which may include, e.g., a first maximallyreflective mirror 272 and a second maximally reflective mirror 274.

FIG. 13 illustrates schematically and partly in block diagram form,according to aspects of an embodiment of the subject matter disclosed, amulti-pass regenerative ring power amplification stage laser system 280in the form of a bow-tie configuration, this may comprise, e.g., achamber 282, a seed laser 284, an injection seeding mechanism 260 and abeam reverser/returner 270, the latter two of which may be configured(angled), e.g., to effect a crossing of an input pass beam 286 and anoutput pass beam 288, e.g., at or near the intersection of therespective longitudinal and lateral center line axes of electrodes (notshown) generating a gain medium by gas discharge between the electrodes,and thus generally at the longitudinal and lateral axes intersection ofthe gain medium. In such an embodiment the angle between the two passesmay be almost imperceptively small so that, in effect the beams 286, 288are almost aligned with the longitudinal center-line axis of thedischarge formed between the electrodes, one of which, e.g., beam 288,may also form the optical axis of the beam 100 of the laser system. Asshown schematically and well out of proportion in the applicable FIGS.in this application neither beam path, e.g., 286, 288 illustrated inFIG. 13 may be shown to extend along the longitudinal centerline axis ofthe electrodes or may be shown from a side view where the longitudinalcenterline axis is not discernible. In practice however, one pass wouldbe very slightly misaligned with the axis and the other essentiallyaligned with it insofar as such alignment is optically achievable andwithin the tolerances allowed for the optical trains of such lasersystems.

FIG. 15 illustrates schematically and partly in block diagram format aplan view of an embodiment 280 such as illustrated in FIG. 13, e.g.,where the MO output laser light pulse beam 62 comes from an MOpositioned above (in the direction perpendicular to the plane of thepaper) the power amplification stage chamber 282. Further, FIG. 16illustrates schematically and partly in block diagram format a side viewof the apparatus 280 of FIGS. 13 and 15. A turning mirror maximalreflector 430 turns the MO laser output light pulse beam 62 into, e.g.,an seed injection mechanism 260 and the crossed (bow-tie) passes 276,278 in the oscillation resonance cavity 424 formed by the rear mirrorbeam returner/reflector 270 (not shown in FIG. 16) and the injectionseed mechanism 270 input/output coupler partially reflective mirror 262to form laser system output light pulse beam 100 immerging through theoptic 262 acting as a usual oscillator cavity output coupler, as is wellknown in the art of gas discharge, laser oscillator cavities with outputcouplers. As can be seen in FIGS. 15 and 16, the MO output beam 62enters the ring power amplification stage oscillation cavity through thepartially reflective mirror 262, which also forms the cavity outputcoupler from a direction, in relation to the axis of the system outputbeam 100 that prevents reverse coupling of the system output beam 100back to the MO.

FIG. 17 illustrates a schematically and partially in block diagramformat an input/output coupling scheme for a single rear mirror cavity300, e.g., with the multi-pass regenerative ring oscillator laser system300, according to aspects of an embodiment of the subject matterdisclosed, in the form of a bow-tie configuration, having, e.g., asingle maximally reflective rear cavity mirror 310. In operation the MOlaser input/output coupler, e.g., an orthogonal seed injection mechanism160 may direct the MO laser output light pulse beam 62 into the cavityformed at the rear by, e.g., a single maximally reflective mirror 310 toform, e.g., a “half” bow-tie configuration having a first pass path 76and a second pass path 78.

Turning now to FIG. 8 there is shown, according to aspects of anembodiment of the subject matter disclosed, what applicants refer to asan OPuS effect cavity 320 in which, e.g., a polarizing beam splitter 322and a maximally reflective rear cavity mirror 324 may be used along witha quarter wave plate 326 and an output coupler 328. The system 320,according to aspects of an embodiment of the subject matter disclosed,may, e.g., due to slight misalignment of optical elements 322 and 324,have multiple passes generated within the oscillator cavity formedbetween the rear mirror 324 and output coupler 328, caused, e.g., by themisalignment.

According to aspects of an embodiment of the subject matter disclosed,the orthogonal seed injection mechanism may comprise an orthogonalinjection seeding optic such as, e.g., optical element 350, illustratedin FIG. 18 schematically and in cross-section across the longitudinalextent of the optic 350. Optical element 350 may be made of, e.g., CaF₂,e.g., uncoated CaF₂, and may comprise, e.g., according to aspects of anembodiment of the subject matter disclosed, an external input/outputinterface facing 352, a total internal reflection face 354, and aninternal input/output interface face 356. In operation, as will beunderstood by those skilled in the optics art, the MO laser output lightpulse beam 62 may be incident upon received by the external input/outputinterface facing 352, e.g., at an incidence angle of, e.g., about 70°and be refracted within the optic 350 as beam 62′ to the total internalreflection face 354, which may be angled so as to totally internallyreflect the beam 62′ onto the internal input/output interface face 356as beam 62″ where it is refracted again upon entering the lasing gasmedium environment inside of the chamber (not shown in FIG. 18), e.g.,along a first path 76 and, after again passing through the gain medium,e.g., after reflection from a beam reverser (not shown in FIG. 18) itagain is incident on and transmits through the face 356, as beam 78 andis refracted within the optic 350 as beam 78′ to exit optic 350 asthrough this external input/output interface facing 352 the laser systemoutput light pulse beam 100. The beams 76, 78 according to aspects of anembodiment of the subject matter disclosed, along with the beam reverser(not shown in FIG. 18), may cross, e.g., as shown in FIG. 13 or not asshown in FIG. 12. It will be understood that the beam 78′ will alsopartially reflect onto the total internal reflecting surface 354 as beam78″ (62′) and the partially reflected portion will become beam 62″ andbeam 76 again, so that the optic 350 acts as an output coupler untilenough oscillations occur such that the stimulated emissions form asubstantial laser system output laser light pulse beam 100.

According to aspects of an embodiment of the subject matter disclosedanother version of a seed injection optic 360, illustrated in FIG. 19,schematically and in cross section across a longitudinal axis thereof,may comprise, e.g., an external input/output interface facing 362, atotal internal reflection face 364 and an internal input/outputinterface face 366. In operation the beam 62 from the MO may be incidentupon the external input/output interface facing 362 and be refractedwithin the optic 360 as beam 62′ to the total internal reflection face364, and be reflected as beam 62″ to the internal input/output interfaceface 366 where it will exit and again be refracted in the gas of thelasing medium environment as beam 76. After return from the beamreverser (not shown in FIG. 19) the beam 78 refracts in the optic 360 asbeam 78′ and transmits through the external input/output face 362 aslaser system output light pulse beam 100. It will also be understood bythose skilled in the laser art, as was so also with the embodiment ofFIG. 18, that the beam 78′ will also partially reflect onto the totalinternal reflecting surface 364 as beam 78″ (62′) and the partiallyreflected portion will become beam 62″ and beam 76 again, so that theoptic 360 acts as an output coupler until enough oscillations occur suchthat the stimulated emissions form a substantial laser system outputlaser light pulse beam 100.

According to aspects of an embodiment of the subject matter disclosed avariety of beam returners/reversers 370 may be utilized, e.g., asillustrated schematically in FIGS. 20-22. The optic 370 of FIG. 20 mayincorporate, e.g., an input/output face 372, a first total internalreflection face 374, a second total internal reflection face 376 and athird total internal reflection face 378, such that, in operation thebeam 76 transiting the gain medium in a first direction may be incidenton the face 372, and be reflected by the faces 374, 376 and 378 to exitthe optic 370 at the input/output interface face 372 as the beam 78passing through the gain medium in a second direction. A similar beamreverser 380 is illustrated in cross section and schematically in FIGS.21 and 22 wherein there are only two totally internal reflectingsurfaces 384, 386 and 394, 396 in the optics 380 and 390 respectively.

It will also be understood by those skilled in the optics art that withthree internal reflections, or with a three mirror arrangement, e.g., asis currently in use as a beam reverser on applicants' assignee's XLAmodel laser systems, the input beam 76 and output beam 78 will beeffectively aligned and parallel and that relationship does not change,e.g., with rotation of the optic, e.g., optic 370, e.g., about an axisperpendicular to the plane of the page of FIG. 20. For the reversers380, 390 respectively of FIGS. 21 and 22, the even number of internalreflections, e.g., two internal reflections allows for the beams 76, 78to have variable angular relationship in the plane of the paper of FIGS.21 and 22.

It will be understood by those skilled in the optics art that variouscombinations of the seed injection mechanism referred to in the presentapplication and beam reversers/returners may be utilized to get thebeams, e.g., on paths 76, 78 to cross, e.g., as illustrated in FIGS. 2,3, 4 and 13 or not, e.g., as illustrated in FIG. 12. Also, manipulatingthese optics will be understood to enable the selection of, e.g., acrossing point for the paths, e.g., 76, 78, e.g., with respect to theextent of the lasing gain medium, e.g., along the longitudinal and/orvertical axis of the lasing gas gain medium during a discharge betweenthe gain medium exciting electrodes. This may be utilized to varyparameters of the ultimate laser system output laser light pulse beampulses, e.g., energy, energy stability and the like.

Turning now to FIG. 23 there is illustrated a snout 140, variousversions of which are illustrated schematically, e.g., in FIGS. 2, 3 and4. The snout 140 may comprise, e.g., a window housing 550, which maycomprise an external mounting plate 552 and housing walls 554 machinedwith the housing plate 552 or otherwise affixed to the housing plate552. Also a window mounting plate 556 is shown. This window housing 550shown illustratively, according to aspects of an embodiment of thesubject matter disclosed, may be similar to such window housingscurrently being used on applicants' assignee's laser systems and mayhave a window housing end plate (not shown in this view for claritypurposes), similar to the laser end plate 570, such as is shown in FIG.23 at the laser side of the snout 140. The not shown window mountinglaser end plate may be at the point of the window mounting plate 556.Similarly the snout 140 may have a window end plate (not shown in thisFIG. for clarity) similar to the end plate 552 to affix the windowhousing 550 to the remainder of the snout 140. The laser chamber endmounting plate 568 may be attached to the laser chamber, e.g., 144 inFIG. 2, by mounting bolts 574, and have an aperture 572 through thebeam, e.g., 76 enters the chamber 144 and beam 78 returns from thechamber 144.

As shown in FIG. 23 partly schematically and partly in block diagramform the beam expander 142, e.g., comprising beam expanding prism 146and beam expanding prism 148, may be within the snout 140, as shownschematically in the cutaway of FIG. 23. At least one of the prisms 146,148 may be mounted on mounts (not shown) for movement one relative tothe other. This may be controlled, e.g., by a controller 600, e.g., byan actuator 580, e.g., a stepper motor or other suitable actuators knownin the art of laser system optic positioning control as referenced inone or more of the above referenced patents or co-pending applications,connected to the respective at least one prism, e.g., prism 148 by anactuator shaft 582, e.g. for rotation of the prism 148 on the axis ofthe shaft 582, to change its position relative to the prism 142 and alsoother optics, e.g., an orthogonal seed injection mechanism (not shown inFIG. 23) and/or the beam returner/reverser (not shown in FIG. 23).

Similarly as illustrated schematically and partly in block diagram form,e.g., in FIGS. 13 and 15, the beam reverser/returner 270 and/or the seedinput/output coupling optic 260 may be controlled by a controller 600controlling the operation of an actuator 590 for the beamreturner/reverser and 594 for the input output optic, e.g., anorthogonal seed injection mechanisms 260, with the actuators 590, 594connected to the controller 600 by control signal lines 592 and 596respectively.

A ring cavity, e.g., with an output coupler seed laser coupling, e.g.,an seed injection mechanism, while perhaps more complex a configuration,makes most efficient use of seed laser energy.

According to aspects of an embodiment of the subject matter disclosed,for the seed laser input/output coupling a range of maximally reflectingmirrors may be utilized, e.g., from about a square 45 degree Rmax toabout a square 30 degree Rmax, e.g., as is used on applicants'assignee's ArF 193 nm LNMs. Reflectivity for P-polarization is onlyabout 85% at 45 degrees.

According to aspects of an embodiment of the subject matter disclosedwhere attenuation of s-polarization may be needed, e.g., because of ASE,it may be achieved via Brewster reflections and insertion of partialreflectors in or into the power amplification stage cavity.

MOPO energy vs. amplification stage timing has been examined atdifferent values of seed laser energy, ArF chamber gas mixture,percentage reflectivity of output coupler (cavity Q) and seed laserpulse duration, with the results as explained in relation to FIG. 7. Themaximum intensity of the seed pulse has been observed to occur duringthe initial, very low level, fluorescence of the amplification stage.This very low level fluorescence (and thus gain) is believed to beenhanced by this seed light, as observed in MOPO output. Adjustment ofthe timing of the seed earlier than or later than, e.g., about 20 or sons before the amplification stage firing can, e.g., lead to an increasein weak line output, an indication of, e.g., when the “primordial”photons are generated in the amplification stage.

ASE vs. MO-PO timing has been examined for different values of seedlaser energy, ArF chamber gas mixture, percentage reflectivity of outputcoupler (cavity Q) and seed laser pulse duration with the results alsoexplained in relation to FIG. 7.

The relationship between forward energy and seed energy has also beenexamined and the results of which are illustrated, e.g., in FIGS. 24 and25. The measurements taken at what was considered to be optimum timingof the discharge in the lasing medium in the MO and the discharge in thelasing medium in the ring power amplification stage. In FIG. 24 thecurves 610 represent forward energy values and the curves 612representing backward energy values, with the square data pointsrepresenting operation with P90+P70 filters and the realignment wasperformed after insertion of partial reflectors with the results asshown in FIG. 25.

ASE can be of great concern with MOPO designs. Improper timing may leadto increased ASE up to and including generations of only ASE when the MOand power amplification stages are so mis-timed that essentially onlybroad band(ASE) lasing occurs in the power amplification stage, whichbeing an oscillator will lase when the discharge occurs between theelectrodes in the power amplification stage. Unlike a power amplifier,such as in applicants assignee's XLA-XXX laser system where the seedbeam passes through the amplification stage a fixed number of timesdepending on the optical arrangement, in systems according to aspects ofan embodiment of the subject matter disclosed amplified spontaneousemission (ASE) lasing occurs whether the seed laser pulse is present foramplification or not. Back scatter from the amplifier cavity optics canform a parasitic laser cavity. Some amplifier cavity optics can form anunintended laser cavity between the amplifier and MO. Therefore, carefulcontrol of timing is used, according to aspects of an embodiment of thesubject matter disclosed, to keep ASE below limits that reduces oreffectively eliminates the unwanted lasing.

ASE measurements have been made with medium and small seed input energy.For example for medium energy, e.g., seed energy of around 50 μJ, with adischarge voltage Vco of around 950V, and with an AMPLIFICATION STAGEgas fill of 38/380, fluorine partial pressure/total pressure, it hasbeen shown that with a relative timing of between about −10 ns and +10ns of optimum the ASE ratio is below about 3×10⁻⁵. With low seed energy,e.g., around 5 μJ, with the same voltage and fill the ASE ratio is keptbelow about 6×10⁻⁴ between about 10 ns to +10 ns of relative timing.

Maintaining proper ASE performance may require selecting properamplifier cavity optics that have appropriate selectivity to eliminateunwanted polarization (e.g., utilizing appropriate coatings/angles ofincidence, etc.), which can result in better suppression of unwantedpolarization, which can result in reduced ASE, e.g., from theS-polarization. Creating dispersion in the amplifier cavity, e.g., withbeam expanding and dispersing prisms has also been determined byapplicants, according to aspects of an embodiment of the subject matterdisclosed, to be an effective method for further reducing the ASE ratiocontributing to an effectively large enough margin against whatever ASEspecification is selected.

According to aspects of an embodiment of the subject matter disclosed amethod is proposed to reduce ASE in ring amplifiers, e.g., to takebetter advantage of other features of this architecture, e.g., low seedenergy, high efficiency, energy stability etc. Applicants propose tointroduce some broad band (at least much broader than the line narrowedseed radiation propagating in the opposite direction from that of themain radiation direction to increase ASE in this direction and reduceASE in the main direction. That is to say broad band gain will beutilized in the opposite path around the ring to reduce the availablegain for ASE in the main direction. This could be accomplished, e.g.,with some scatter of the seed laser beam from the optics, e.g., byfeeding florescence of the seed laser into the ring power amplificationstage. The broad band emission can thereby, e.g., deplete gain availableto the ASE and will be propagated oppositely to main radiationdirection, reducing broad band emission in the main direction.

According to aspects of an embodiment of the subject matter disclosed itwill be understood that solid state pulsed power systems such as themagnetically switched systems noted above in one or more of thereferenced patents or patent applications and as sold with applicants'assignee's laser systems, having very tightly controlled timing of thefirings of electric discharges between electrodes in the respective MOand amplification gain medium chambers, along with the properties of aring power amplification stage in a MOPRO configuration (e.g., operatingthe ring power amplification stage at or very near total saturation),enables the delivery to a lithography tool or an LTPS tool, or the like,laser system output light pulse beam pulses having about twice the dosestability as is currently achievable, e.g., in applicants' assignee'sXLA MOPA laser systems.

FIG. 26 shows schematically and in block diagram an energy/dose controlsystem 620 according to aspects of an embodiment of the subject matterdisclosed. As illustrated in block diagram form, the energy/dosecontroller 620 may include a solid state pulsed power system 624, suchas a magnetically switched pulsed power system as noted above, which maybe controlled, e.g., by a timing and energy control module 622 of thetype sold with applicants' assignee's current laser systems, e.g., XLAMOPA configured laser systems and discussed in one or more of the abovereferenced patents or co-pending applications. Such timing end energycontrol modules in combination with the SSPPM 624 are capable of veryfine pulse to pulse energy control, e.g., out of the MO and very fine,e.g., within a few nanoseconds, control of the relative timing of thefiring of the electric discharge between a first pair of electrodes (notshown) in the MO 24 and a second pair of electrodes, e.g., electrodes424 in the amplification stage 144 as illustrated, e.g., in FIGS. 15 and16. This enables, as discussed in one or more of the above referencedpatents and co-pending applications, e.g., the selection of a portion ofthe output laser light pulse beam pulse from the MO to initiate seedingof the amplification gain medium and the like, e.g., to controlbandwidth and also impact other overall laser system output light pulsebeam pulse parameters. This, in combination with the ring poweroscillator operating at or nearly at saturation, e.g., within about5-10% of saturation, or closer enables the system to delivery abouttwice the dose stability as is currently available in, e.g., lithographylaser light sources, such as applicants' assignee's XLA laser systems orexisting laser annealing light sources, e.g., for LTPS.

Referring to FIG. 31, a beam mixer/flipper 1050 is shown for operationon a beam 1052 (which for illustrative purposes has been shown as havingan upper white half and a lower black half). As explained in greaterdetail below, the beam mixer 1050 can be used to alter the intensityprofile of a beam, e.g. improving intensity symmetry along a selectedaxis of a beam, and can be used to reduce beam coherency, or both. Forthe embodiment shown, the beam mixer 1050 includes a beam splitter 1054and mirrors 1056 a-c.

For the arrangement shown in FIG. 31, the beam 1052 can be initiallyincident upon the beam splitter 1054 whereupon a portion of the beam maydirected, via reflection, toward mirror 1056 a and the remainder istransmitted, (e.g., with substantially no change in direction) throughthe beam splitter 1054 and exits the beam mixer 1050 on an output beampath 1070. In one setup, a beam splitter 1054 reflecting about forty tosixty percent of the incident light, e.g., fifty percent, may be used.For this setup, about fifty percent of the initial beam incident uponthe beam splitter 1054 is directed toward the mirror 1056 a. For thebeam mixer 1050, mirrors 1056 a-c may typically be flat, maximumreflectivity mirrors. As shown in FIG. 31, mirror 1056 a may bepositioned and oriented to receive light from the beam splitter 1054 atan angle of incidence of approximately thirty degrees. As further shown,mirror 1056 b may be positioned and oriented to receive light reflectedfrom mirror 1056 a at an angle of incidence of approximately thirtydegrees, and mirror 1056 c may be positioned and oriented to receivelight reflected from mirror 1056 b at an angle of incidence ofapproximately thirty degrees.

Continuing with FIG. 31, light reflected from mirror 1056 c can be madeto be incident upon the beam splitter 1054 at an angle of incidence ofabout forty-five degrees. For a fifty percent reflectivity beamsplitter, about half of the light from mirror 1056 c is reflected ontothe output beam path 1070 and about half of the light from mirror 1056 cpasses through the beam splitter 1054 on a beam path toward mirror 1056a, as shown. Thus, the output beam path 1070 includes a combined beamcontaining the portion of the initial beam 1052 that passed through thebeam splitter 1054 and the portion of light from mirror 1056 c that isreflected from the beam splitter 1054. Similarly, the light on the pathfrom the beam splitter 1054 to mirror 1056 a includes a combined beamcontaining the portion of the initial beam 1052 that is reflected by thebeam splitter 1054 and the portion of light from mirror 1056 c that istransmitted through the beam splitter 1054.

The beam entering the beam mixer 1050 in FIG. 31 is shown illustrativelyas having a rectangular cross-section that defines a long axis 1058.This type of beam is typical of a laser beam produced by an excimerlaser with the long axis corresponding to the direction from onedischarge electrode to the other. A typical beam may have dimension ofabout 3 mm by 12 mm. Moreover, for the output of an excimer laser, theintensity profile in one axis, e.g., the long axis 1058 is typicallyunsymmetrical, whereas the intensity profile in the other axis, e.g.,the short axis (i.e. the axis normal to the long axis 1058) isapproximately Gaussian. Although the beam mixer 1050 shown isparticularly suitable for improving symmetry of a high power excimerdischarge laser, it is to be appreciated that it can be used inconjunction with other types of laser systems and for otherapplications, for example, the beam mixer may be used to reducecoherency in a beam generated by a solid state laser.

FIG. 31 shows that the beam extends along the axis 1058 from a firstedge 1060 to a second edge 1062. FIG. 31 also shows that the mirrors1056 a-c establishing a spatially inverting path which has a beginning1064 and an end 1066. As FIG. 31 illustrates, the inverting path may becharacterized in that a part of the beam near the first beam edge 1060at the beginning 1064 of the inverting path translates to the secondbeam edge at the end 1066 of the inverting path. More specifically, forthe mixer 1050 shown, a photon at the ‘top’ of the beam which strikesmirror 1056 a translates and leaves mirror 1056 c at the ‘bottom’ of thebeam. Since the inverting path constitutes a delay path, there will besome temporal stretching of the pulse, and this can be beneficial,especially in embodiments with the coherence busting mechanism betweenthe master oscillator/seed laser and the amplification gain medium,e.g., the ring power amplification stage. The pulse stretching betweenthe seed laser and amplification gain medium can stretch somewhat thepulse out of the amplification gain medium. This can also be minimized,e.g., by minimizing the delay path, e.g., to a length of about a ns orso. with a suitable delay path time, etc., as noted elsewhere, the beammixer 1050 could form a coherence buster mini-OPuS, e.g., as discussedin regard to FIG. 48.

The beam mixer 1050 may be placed in between the seed beam laser portionand the amplifier laser portion of a MOPA or MOPRO (with, e.g., a ringpower amplification stage), configured multi-chambered laser system,such as that shown in FIGS. 1-6 and 9-16. Other forms of coherencybusting, of the passive type, may be used, e.g., between the MO and PAas discussed in above referenced in U.S. patent application Ser. No.11/447,380, entitled DEVICE AND METHOD TO STABILIZE BEAM SHAPE ANDSYMMETRY FOR HIGH ENERGY PULSED LASER APPLICATIONS, filed on Jun. 5,2006, and Ser. No. 10/881,533, entitled METHOD AND APPARATUS FOR GASDISCHARGE LASER OUTPUT LIGHT COHERENCY REDUCTION, filed on Jun. 29,2004, and published on Dec. 29, 2005, Pub. No. 20050286599, as well asSer. No. 11/521,904, entitled LASER SYSTEM, filed on the same day as thepresent application, referenced above.

The darker and lighter entry beam portions as shown in FIG. 31 may beseparate beams from separate sources, spatially separated, and the beammixer 1050 can act as such in addition to or in lieu of being used as acoherency buster for a single beam.

It will be understood that several possible embodiments of delay pathscomprising beam mixers, coherence busters or both are illustrated in thepresent application but are not exhaustive of the optical delay pathsthat cam be employed, e.g., those having imaging mirrors and not havingimaging mirrors, or having a mixture of both, that perform beam delay,flipping and/or mixing functions, provided that, at a minimum the beampulses (including daughter pulses) are flipped/mixed (or both) withrespect to the main pulse and other daughter pulses.

It will be understood by those skilled in the art that as disclosed inthe present application according to aspects of an embodiment of thesubject matter disclosed, applicants have enabled the satisfaction ofcustomer demands, both from scanner makers and semiconductormanufacturer end users, that have been placed on light source suppliers,e.g., ArF light sources, beyond even the traditionally expected powerand bandwidth improvements. For example, further CoC Improvement isdemanded because, e.g., ArF is now used in high volume production, e.g.,on cost sensitive products, the industry expectation of equivalentreductions in cost of operation and thus cost of consumables for ArF aswas historically demanded in KrF as that technology matured. Inaddition, energy stability improvements are met by the subject matterdisclosed, e.g., critical dimension variation sensitivity to dose, whichhas become greater with the advent of low K1 lithography techniques. Thedouble exposure concept, e.g., also trades off between overlay and dosecontrol. Optical maskless lithography will require single pulse exposurecontrol, improved by aspects of embodiments of the subject matterdisclosed.

With regard to energy stability improvements, the Cymer XLA light sourceled to a significant improvement in energy stability by exploiting thesaturation effects in the PA of a MOPA configuration, e.g., with a twopass PA amplification. The slope of Eout vs. Ein for XLA is about ⅓. MOenergy instabilities are reduced by a factor of 3× when passed throughsuch a PA. However, even with the 3× improvement through the PA, theMOPA system energy stability is still greatly impacted by, e.g., the MOenergy instability. MO and PA contributions are about equal. Othercontributions such as, voltage regulation, timing jitter, and MOpointing jitter are relatively smaller contributors, but notinsignificant. The PA energy stability performance falls somewherebetween a typical broadband oscillator and a fully saturated amplifier.

According to aspects of an embodiment of the subject matter disclosed, arecirculating ring configuration, e.g., a power ring amplificationstage, operates in a much stronger region of saturation. The slope ofEout vs. Ein for a seed laser/amplification gain medium system, e.g.,with a ring power amplification stage has been measured by applicants'employer at 0.059. MO energy instabilities can be reduced by a factor of17×, e.g., when passed through a recirculating ring oscillator, e.g., apower ring amplification stage.

With the recirculating ring configuration the amplification stage energystability will exhibit the characteristics of a fully saturatedamplifier. Applicants expect at a minimum to see about a 1.5-2×improvement in energy stability.

$\sigma_{System} = \sqrt{{\frac{1}{17}\sigma_{MO}^{2}} + \sigma_{PA}^{2} + \sigma_{voltage}^{2} + \sigma_{timing}^{2} + \sigma_{{MO}\mspace{14mu}{Pointing}}^{2}}$

It will further be understood by those skilled in the art that accordingto aspects of an embodiment of the subject matter disclosed a power ringamplification stage may be utilized. Optics may be utilized to createtwo or more overlapping bow ties or race tracks for four passes peroscillation in the cavity.

Characteristic of such amplifier media, e.g., regenerative orrecirculating ring power amplification stage can include parallelplanarity which could be a stable oscillator, e.g., in half planes or anunstable oscillator. The beam returner/beam reverser could utilizemultiple mirrors or prisms or a combination thereof, positioned insideor outside the chamber or a combination thereof, e.g., dependant uponexposure to certain levels of energy density by one or more of theoptical elements. Unwanted light, e.g., mostly ASE is discriminatedagainst in a variety of ways, e.g., preferentially being created in adirection opposite from the regeneration path of the oscillations of theseed laser pulse beam, e.g., in the ring power amplification stage.

Expanding the beam within the amplifier stage cavity, e.g.,corresponding to the vertical direction of a Brewster angle window, alsocan serve to protect optical elements in the ring power oscillatorcavity as well as disperse the light to lessen ASE. The output couplerportion of the seed inject mechanism may, e.g., have a reflectivity ofaround 20% for the desired (in-band) frequencies (or polarization orboth). Beam expansion may also be able to be performed with multipleprisms, some one or more of which may be inside and/or outside of thechamber enclosure. That is, while one or more of such prisms may beinside the chamber enclosure and exposed to the fluorine containinglaser gas mixture, at least one may also be outside the chamber.

Turning now to FIG. 7 there is shown a chart illustrating by way ofexample a timing and control algorithm according to aspects of anembodiment of the subject matter disclosed. The chart plots laser systemoutput energy as a function of the differential timing of the dischargein the seed laser chamber and the amplification stage, e.g., the ringpower amplification stage as curve 600, which is referred to herein asdtMOPO for convenience, recognizing that the amplification stage in someconfigurations may not strictly speaking be a PO but rather a PA thoughthere is oscillation as opposed to the fixed number of passes through again medium in what applicants' assignee has traditionally referred toas a power amplifier, i.e., a PA in applicants' assignee's MOPA XLA-XXXmodel laser systems, due, e.g., to the ring path length's relation tothe integer multiples of the nominal wavelengths. Also illustrated is arepresentative curve of the ASE generated in the amplification stage ofthe laser system as a function of dtMOPO, as curve 602. In addition,there is shown an illustrative curve 604 representing the change in thebandwidth of the output of the laser system as a function of dtMOPO.Also illustrated is a selected limit for ASE shown as curve 606.

It will be understood that one can select an operating point on the ASEcurve at or around the minimum extremum and operate there, e.g., bydithering the control selection of dtMOPA to, e.g., determine the pointon the operating curve 602 at which the system is operating. It can beseen that there is quite a bit of leeway to operate around the minimumextremum of the ASE curve 602 while maintaining output pulse energy onthe relatively flat top portion of the energy curve to, e.g., maintainlaser system output pulse energy and energy σ, and the related dose anddose σ constant, within acceptable tolerances. In addition as shown,there can be a concurrent use of dtMOPO to select bandwidth from a rangeof bandwidths while not interfering with the E control just noted.

This can be accomplished regardless of the nature of the seed laserbeing used, i.e., a solid-state seed or a gas discharge laser seed lasersystem. Where using a solid-state seed laser, however, one of a varietyof techniques may be available to select (control) the bandwidth of theseed laser, e.g., by controlling, e.g., the degree of solid-state seedlaser pumping. Such pump power control may, e.g., put the pumping powerat above the lasing threshold in order to select a bandwidth. Thisselection of bandwidth may shift or change the pertinent values of thecurve 604, but the laser system will still be amenable to the type of Eand BW control noted above using dtMOPO to select both a BW andconcurrently an operating point that maintains the output energy of thelaser system pulses at a stable and more or less constant value in theflat top region of the illustrated energy curve 600. It is also possibleto use a non-CW solid state seed laser and to adjust the outputbandwidth. For example, selection of the output coupler reflectivity ofthe master oscillator cavity (cavity-Q) can adjust the output bandwidthof the seed laser system. Pulse trimming of the seed laser pulse mayalso be utilized to control the overall output bandwidth of the lasersystem.

It can be seen from FIG. 7 that either the selected ASE upper limit orthe extent of the portion of the energy curve that remains relativelyflat with changes in dtMOPO may limit the range of available bandwidthfor selection. The slope and position of the BW curve also can be seento influence the available operating points on the ASE curve to maintainboth a constant energy output and a minimum ASE while also selectingbandwidth from within an available range of bandwidths by use of theselection of a dtMOPO operating value.

It is similarly known that the pulse duration of discharge pulses in agas discharge seed laser, among other things, e.g., wavefront controlmay be used to select a nominal bandwidth out of the seed laser and thusalso influence the slope and/or position of the BW curve 604 asillustrated by way of example in FIG. 7.

Turning now to FIG. 28, there is shown an example in schematic and blockdiagram form of a laser system controller 620, according to aspects ofan embodiment of the subject matter disclosed. The controller 620 maycomprise part of a laser system including, e.g., a seed laser 622, suchas a gas discharge laser known in the art of the type XeCl, XeF, KrF,ArF or F₂ or the like, which may have associated with it a linenarrowing module 624, as is known in the art, for selecting a particularnominal center wavelength and at the same time narrowing the bandwidthto the ranges discussed above in the present application. The seed laser622 may produce a seed laser output beam 626, which may pass through abeam splitter 630 which diverts a small portion of the output beam 626to a metrology unit metrology module 632, which may include, among otherthings, an MO energy detector and a wavemeter, measuring, e.g., centerwavelength and bandwidth.

The output beam 626 may then be turned by a maximally reflective mirror634 (for the nominal center wavelength) to a seed injection mechanism636. The seed injection mechanism may include, e.g., a partiallyreflective optical element 638 and a maximally reflective opticalelement 640, and may be two separate elements or a single optic asdiscussed elsewhere in the present application. As discussed elsewhere,the seed injection mechanism may inject the seed laser output pulse beam626 into an amplification gain medium, such as a ring poweramplification stage 650 along an injection path 652. A beam splitter 654can divert a small portion of the output beam 658 into a metrology unit656 which may measure, e.g., output energy and bandwidth. A metrologyunit 642 connected directly to the amplification gain medium laser 650which can measure, e.g., ASE in the laser chamber 650.

A controller 660, which may comprise a processor 662, receives inputsfrom the various metrology units 632, 642 and 656, and others asappropriate, and utilize them as part of control algorithms referencedin one or more of the above noted patents and co-pending applicationsand also incorporate the control algorithm noted above regardingoperating at or around the ASE curve minimum while maintaining energyconstant and also selecting bandwidth within the limits imposed by aselected ASE limit. In addition, as is shown in one or more of the abovereferenced patents and co-pending applications the controller 660 mayalso control the timing of the creation of an output pulse in the seedlaser and the creation of the output pulse in the amplification gainmedium (dtMOPO for short) and also provide control signals to the linenarrowing module, e.g., to control bandwidth, e.g., by wavefrontmanipulation or optical surface manipulation as discussed above and inone or more of the above referenced patents and co-pending patentapplications.

Turning now to FIG. 29 there is illustrated schematically and in blockdiagram form a laser system 680 like that of the laser system 620 ofFIG. 28 with the exception that the seed laser 682 is, e.g., a solidstate seed laser with an associated frequency converter 684 to, e.g.,modify the wavelength of the output of the seed laser 682 to awavelength suitable for amplification in the amplification gain mediumstage 650. In addition, the controller 660 may provide inputs to theseed laser 682 to control both the timing of the creation of the seedlaser pulse and the bandwidth, e.g., by modifying the pumping power, asdiscussed above.

According to aspects of an embodiment of the subject matter disclosedone may need to select an edge optic that is an optic that may have tobe used, and thus perhaps coated, all the way to its edge, which can bedifficult. Such an optic could be required, e.g., between the outputcoupler, e.g., 162 shown in FIG. 2 and the maximum reflector, e.g., 164,shown in FIG. 2, together forming a version of a seed injectionmechanism 160, shown in FIG. 2, e.g., depending upon the separationbetween the two, since there may be too little room to avoid using anedge optic. If so, then the edge optic should be selected to be theRmax, e.g., because of the ray path of the exiting beam as it passesthrough the OC portion 162. From a coatings standpoint it would bepreferable to have the OC be the edge optic because it has fewer layers.However, an alternative design, according to aspects of an embodiment ofthe subject matter disclosed has been chose by applicants and isillustrated schematically and by way of example in FIG. 30, e.g.,wherein the use of an edge optic can be avoided, e.g., if a large enoughspacing is provided between out-going and in-coming ring poweramplification stage beams, e.g., as created by the beam expander, 142shown in FIG. 2, e.g., prisms 146, 148. For example, about a 5 mmspacing between the two beams has been determined to be satisfactoryenough to, e.g., to avoid the use of any edge optics.

As illustrated by way of example in FIG. 30 the laser system, e.g.,system 110 illustrated by way of example in FIG. 2, may produce a lasersystem output pulse beam 100. e.g., using a ring power amplificationstage 144 to amplify the output beam 62 of a master oscillator 22 in aring power amplification stage 144. A beam expander/disperser 142, shownin more detail by way of an example of aspects of an embodiment of thesubject matter disclosed may be comprised of a firstexpansion/dispersion prism 146 a, and a second expansion/dispersionprism 146 b, and a third prism 148.

The seed injection mechanism 160 may comprise a partially reflectiveinput/output coupler 162, and a maximally reflective (Rmax) mirror 164,illustrated by way of example and partly schematically in FIG. 30 in aplan view, i.e., looking down on the seed injection mechanism and mexpansion/dispersion 160 and the ring power amplification stage chamber(not shown) into and out of which, respectively the beams 74 and 72traverse, that is from the perspective of the axis of the output beam 62traveling from the master oscillator chamber 22, which in such anembodiment as being described may be positioned above the chamber 144(the beam 62 having been folded into the generally horizontallongitudinal axis as shown (the beam also having been expanded in theMOPuS in its short axis, as described elsewhere, to make it generally asquare in cross-sectional shape.

With regard to the configuration of the beam expansion prisms 146 a, 146b and 148 inside the ring power amplification stage cavity a similararrangement may be provided to that of the beam expansion on the outputof the power amplifier (“PA”) stage in applicants' assignee's XLA-XXXmodel laser systems, e.g., with a 4× expansion, e.g., provided by a68.6° incident and 28.1° exit, e.g. on a single prism or on two prismswith the same incident and exit angles. This can serve to, e.g., balanceand minimize the total Fresnel losses. Reflectivity coatings, e.g.,anti-reflectivity coatings may be avoided on these surfaces since theywill experience the highest energy densities in the system. According toaspects of an embodiment of the subject matter disclosed the beamexpander/disperser 160 may be implemented with the first prism 146 splitinto to small prisms 146 a, and 146 b, which may be, e.g., 33 mm beamexpander prisms, e.g., truncated, as shown by way of example in FIG. 30,to fit in the place where one similarly angled prism could fit, with thesplit prism having a number of advantages, e.g., lower cost and theability to better align and/or steer the beams 72, 74 (in combinationwith the beam reverser (not shown in FIG. 30) and the system output beam100.

The master oscillator seed beam 62 may enter the seed injectionmechanism 160 through the beam splitter partially reflective opticalelement 162, acting as an input/output coupler, to the Rmax 164 as beam62 a, from which it is reflected as beam 74 a to the first beam expanderprism 146 a, which serves to de-magnify the beam in the horizontal axisby about ½× (it remains about 10-11 mm in the vertical axis into theplane of the paper as shown in FIG. 30). The beam 74 b is then directedto the second beam expansion prism 148, e.g., a 40 mm beam expansionprism, where it is again de-magnified by about ½× so the totalde-magnification is about ¼× to form the beam 74 entering the gainmedium of the ring power amplification stage (not shown in FIG. 30. thebeam is reversed by the beam reverser, e.g., a beam reverser of the typecurrently used in applicants' assignee's XLA-XXX model laser system PAsand returns as beam 72 to the prism 148, e.g., having crossed in thegain medium in a bow-tie arrangement or having traveled roughlyparallel, perhaps overlapping to some degree in a version of arace-track arrangement. From prism 148 where the beam 72 is expanded byroughly 2× the beam 72 b is directed to prism 142 b and is expanded afurther approximately 2× into beam 72 a. Beam 72 a is partiallyreflected back to the Rmax as part of beam 62 a and is partiallytransmitted as output, beam 100, which gradually increases in energyuntil an output beam pulse of sufficient energy is obtained by lasingoscillation in the ring power amplification stage. The narrowing of thebeam entering the amplification gain medium, e.g., the ring poweramplification stage has several advantageous results, e.g., confiningthe horizontal widths of the beam to about the width of the electricalgas discharge between the electrodes in the gain medium (for a bow-tiearrangement the displacement angle between the two beams is so smallthat they each essentially stay within the discharge width of a few mmeven thought they are each about 2-3 mm in horizontal width and for therace track embodiment, the bean 72 or the bean 72 only passes throughthe gain medium on each round trip, or the beams may be furthernarrowed, or the discharge widened, so that both beams 72,74 passthrough the discharge gain medium in each round trip of the seed beams72, 74.

The positioning and alignment of the prisms 146 a, 146 b and 148,especially 146 a and 146 b can be utilized to insure proper alignment ofthe output beam 100 from the ring power amplification stage into thelaser output light optical train towards the shutter. The beam leavingthe input/output coupler 162 may be fixed in size, e.g., in thehorizontal direction, e.g., by a horizontal size selection aperture 130,forming a portion of the system aperture (in the horizontal axis) toabout 10.5 mm. Another aperture, e.g., in the position roughly of thepresent PA WEB, e.g., in applicants' assignee's XLA-XXX laser systemproducts, can size the beam in the vertical dimension. According toaspects of an embodiment of the subject matter disclosed applicantspropose that a system limiting aperture be positioned just after themain system output OPuS, e.g., a 4×OPus. A ring power amplificationstage aperture may be located about 500 mm further inside the lasersystem. This distance is too great to avoid pointing changes turninginto position changes at the specified measurement plane (present systemaperture). Instead the limiting system aperture can be located justafter the OPuS, and may have a 193 nm reflecting dielectric coatinginstead of a stainless steel plate commonly used. This design can allowfor easier optical alignment, while at the same time reduce heating ofthis aperture.

According to aspects of an embodiment of the subject matter disclosed,applicants propose to implement a relatively stress-free chamber windowarrangement similar to or the same as that discussed in the abovereferenced co-pending U.S. patent application, because of the use of,e.g., a PCCF coated window.

According to aspects of an embodiment of the subject matter disclosed,applicants propose to, e.g., place ASE detection, e.g., backwardpropagation ASE detection, in either the LAM or in an MO wavefrontengineering box (“WEB”), which can, e.g., include elements of the MOWEBfrom applicants' assignee's existing XLA-XXX model laser systems alongwith the mini-OPuSs discussed elsewhere in this application referencedherein, as well as, e.g., beam expansion, e.g., using one or more beamexpansion prisms to expand the output beam of the MO in its short axis,e.g., to form generally a square cross-sectional beam. The current MOWEB and its beam turning function is represented schematically as theturning mirror, e.g., 44 shown in FIG. 2. As a preference, however, thebackward propagation detector may be placed “in” the MO WEB/MOPuS, thatis, e.g., by employing a folding mirror (fold #2), e.g., 44 in FIG. 2,with, e.g., a reflectivity of R=95% instead of R=100% and monitoring theleakage through this mirror 44. Some drift and inaccuracy of thisreading may be tolerated, e.g., since it may be utilized as a tripsensor (i.e. measurements in the vicinity of 0.001 mJ when conditionsare acceptable—essentially no reverse ASE—as opposed to around 10 mJwhen not acceptable—there is reverse ASE), e.g., when the ring poweramplifier is not timed to amplify the seed pulse, but still createsbroad band laser light. Existing controller, e.g., TEM controller,cabling and ports and the like for new detectors may be employed. Thedetector may, e.g., be the detector currently used by applicants'assignee on existing XLA-XXX model laser systems to measure beamintensity, e.g., at the laser system output shutter.

According to aspects of an embodiment of the disclosed subject matterone or more mini-OPuS(s), which may be confocal, such that they arehighly tolerant to misalignment and thus of potentially low aberration,e.g., for the off-axis rays needed in the proposed short OPuS(s), theso-called mini-OPuS, can have delay times of 4 ns and 5 ns respectively,where more than one is employed. These values were chosen so that bothOPuSs exhibit low wavefront distortion with spherical optics in additionto appropriate delay paths for coherence busting. The low wavefrontrequirement may actually prevent significant speckle reduction from themini-OPuS(s) unless an angular fan-out from the output of themini-OPuS(s) is generated, e.g., by replacing a flat/flat compensatingplate with a slightly wedged plate, so that the transmitted beam and thedelayed beam in the mini-OPuS are slightly angularly offset from eachother. The laser beam, e.g., from the master oscillator is partiallycoherent, which leads to speckle in the beam. Angularly offsetting thereflected beam(s) reentering the mini-OPuS output with the transmittedbeam, along with the delay path separation of the main pulse into themain pulse and daughter pulses, can achieve very significant specklereduction, e.g., at the wafer or at the annealing workpiece, arisingfrom the reduction in the coherence of the laser light source pulseilluminating the workpiece (wafer or crystallization panel). This can beachieved, e.g., by intentionally misaligning the delay path mirrors,probably not possible with a confocal arrangement, but also with theaddition of a slight wedge in the delay path prior to the beam splitterreflecting part of the delayed beam into the output with the transmittedbeam and its parent pulse and preceding daughter pulses, if any. Forexample, a 1 milliradian wedge in the plate will produce an angularoffset in the reflected daughter pulse beam of 0.86 milliradians.

The optical delay path(s) of the mini-OPuS(s) may have other beneficialresults in terms of laser performance and efficiency. According toaspects of an embodiment of the disclosed subject matter, as illustratedschematically in FIG. 48, the laser beam, e.g., seed beam 500 from theseed source laser (not shown in FIG. 48), may be split into two beams502, 504 using a partially reflective mirror (beam splitter) 510. Thismirror 510 transmits a percentage of the beam into the main beam 502 andreflects the rest of the beam 500 as beam 504 into an optical delay path506. The part 502 that is transmitted continues into the rest of thelaser system (not shown in FIG. 48). The part 504 that is reflected isdirected along a delay path 506 including, e.g., mirrors 512, 514 and516, with mirror 514 being displaced perpendicularly to the plane of thepaper in the schematic illustration, in order to allow the main beam 502to reenter the rest of the laser system, e.g., to form a laser outputbeam or for amplification in a subsequent amplification stage. The beam504 may then be recombined with the transmitted portion 502 of theoriginal beam 500. The delayed beam 504 may be passed through a wedge(compensator plate) 520 essentially perpendicularly arranged in the pathof beam 504. Thus, the daughter pulse beam(s) 504 from the delay path506 are slightly angularly displaced from the main part of the beam inthe transmitted portion 502 in the far field. The displacement may be,e.g., between about 50 and 500 μRad.

The length of the delay path 506 will delay the beam pulses so thatthere is a slight temporal shift between the part of the beam that istransmitted and the part that is reflected, e.g., more than thecoherence length, but much less than the pulse length, e.g., about 1-5ns. By selecting the appropriate path length, which determines the delaytime, the addition of the two beams can be such that the energy in thepulse is spread into a slightly longer T_(is), which in combination withlater pulse stretching in the main OPuS(s) can improve laserperformance, as well as providing other beneficial laser performancebenefits.

Two mini-OPuSs may be needed to achieve the desired effect. The offsettime between the pulses from the two mini-OPuss may be, e.g., onenanosecond. Based upon optical and mechanical considerations, the delaysselected for the stretchers may be, e.g., a 3 ns delay path in the firstmini-OPus and a 4 ns delay path in the second. If the delay is shorter,the optical system, e.g., if it uses confocal or spherical mirrors canintroduce unacceptable aberrations. If the delay is longer, it may bedifficult to fit the system into the available space in the lasercabinet. The distance the beam must travel to achieve the 3 ns delay is900 mm and to delay by 4 ns is 1200 mm. A confocal optical system 520,minimizing the sensitivity to misalignment, illustrated schematically inFIG. 49 may consist of two mirrors 522, 524, whose focal points arelocated at the same position in space and whose center of curvatures arelocated at the opposite mirror, along with a beam splitter 526. Acompensator plate 530 (e.g., a wedge) can be added to insure that thereflected beam and the transmitted beam are slightly misaligned as notedabove with respect to FIG. 48. In this case, the compensator plate isplaced in the path of the delayed beam at an angle for properfunctioning.

Turning now to FIG. 50 there is shown schematically and in block diagramform a line edge/line width roughness (feature dimension roughness)control (reduction and/or selection) system 1350 according to aspects ofan embodiment of the disclosed subject matter. The system 1350 mayinclude a laser light source 20, such as disclosed in the presentapplication and/or above noted patent applications filed concurrentlywith the present application, providing exposure illuminating DUV lightto an illuminating light entrance opening 1352 in a photolithographytool 90. the tool 90, e.g., a scanner, may include an illuminator 92 asis well known in the art, illuminating a mask/reticle 94 for purposes ofexposing an integrated circuit wafer (not shown), e.g., placed on awafer holding stage 94 within the tool 90. Intermediate the illuminator92 and the wafer handling stage 94 may be inserted a coherence bustingmechanism 1370 such as one or more of the types disclosed in the presentapplication and/or in the above noted patent applications filedconcurrently with the present application, e.g., a mini-OPuS. Theilluminator may include a projection lens (not shown) having the abovenoted properties.

The system may also include a sensor, e.g., an image contrast sensor1372, which can be arranged to detect the impact of speckle on thepatterning of an integrated circuit as a whole, or portions thereof, orin selected axes, e.g., one generally parallel to main feature dimensionextending in one axis of the integrated circuit and one in another axis,e.g., generally orthogonal to the first axis. the sensor output may beprovided to a controller 1374, which may be part of the control systemfor the laser or the scanner or an overall control system for both thelaser and scanner, and may provide a control signal, based on thefeedback from the sensor 1372 to the coherence busting mechanism. Thecontrol signal may alter the operation of the coherence bustingmechanism, e.g., by modifying the actuation signals for, e.g., a beamsweeping mechanism(s) in either or both axes, of modifying the positioncompensation plates 520, 532 in the mini-OPuS as discussed above, e.g.,in regard to FIGS. 47-48, e.g., to change the angular displacement ofthe main and daughter pulses, e.g., in one or both axes, i.e., bydiffering amounts and/or directions in each of at least two correctionplates, each contained in separate mini-OPuS arranged in series as notedabove.

Turning now to FIG. 51 there is illustrated schematically and in blockdiagram form a line edge/line width roughness (feature dimensionroughness) control (reduction and/or selection) system 1400, accordingto aspects of an embodiment of the disclosed subject matter, similar tothat of FIG. 50, however, with the coherence busting mechanismintermediate the light source light entry opening 1352 and theilluminator 92. Similarly, there is shown in FIGS. 52 and 53,schematically and in block diagram form, a line edge/line widthroughness (feature dimension roughness) control (reduction and/orselection) system according to aspects of an embodiment of the disclosedsubject matter, wherein the controller 1374 (not shown in FIG. 52 or 53,e.g., within the tool 90, provides a control signal to a coherencybusting mechanism 1454 in FIG. 52 and 1462 in FIG. 53, within arespective laser system 1450 in FIG. 52 or 1460 in FIG. 53, wherein ineach figure the coherence busting mechanism is shown intermediate apulse stretching OPuS 1452 and the lithography tool 92 in FIG. 52 andintermediate the laser light source 20 and the pulse stretching OPuS1462 in the laser system 1460 of FIG. 53.

The delay path time(s) in the mini-OPuS(s) for coherence busting andother purposes may be as short as about the temporal coherence lengthand as long as practical due to the noted optical and spaceconsiderations, such as misalignment and aberration tolerance. If thereare two or more mini-OPuSs then the delay path in each must be differentin length, e.g., by more than the coherence length and selected suchthat there is no significant coherence reaction (increase) due to theinteraction of daughter pulses from the separate OPuS(s). For examplethe delay path times could be separated by at least a coherence lengthand by not more than some amount, e.g., four or five coherence lengths,depending on the optical arrangement.

According to aspects of an embodiment of the subject matter disclosedapplicants propose to employ a coherence-busting optical structure that,e.g., generates multiple sub-pulses delayed sequentially from a singleinput pulse, wherein also each sub-pulse is delayed from the followingsub-pulse by more than the coherence length of the light, and inaddition with the pointing of each sub-pulse intentionally chirped by anamount less than the divergence of the input pulse. In additionapplicants propose to utilize a pair of coherence-busting optical delaystructures, where the optical delay time difference between the pair ofoptical delay structures is more than the coherence length of the inputlight. Each of the two optical delay structures may also generatesub-pulses with controlled chirped pointing as noted in regard to theaspects of the previously described coherence busting optical delaystructure.

According to aspects of an embodiment of the disclosed subject mattertwo imaging mini-OPuSs, which may be confocal, such that they are highlytolerant to misalignment and thus of potentially low aberration, e.g.,for the off-axis rays needed in the proposed short OPuSs, the so-calledmini-OPuSs, and can have delay times of 4 ns and 5 ns respectively.These values were chosen so that both OPuSs exhibit low wavefrontdistortion with spherical optics. The low wavefront requirement mayprevent significant speckle reduction from the mini-OPuSs unless anangular fan-out from the mini-OPuSs is generated, e.g., by replacing aflat/flat compensating plate with the slightly wedged plate.

It will be understood by those skilled in the art that according toaspects of an embodiment of the disclosed subject matter, adequatecoherence busting may be achieved sufficiently to significantly reducethe effects of speckle on the treatment of a workpiece being exposed toillumination from the laser system, such as in integrated circuitphotolithography photoresist exposure (including the impact on line edgeroughness and line width roughness) or laser heating, e.g., for laserannealing of amorphous silicon on a glass substrate for low temperaturerecrystallization processes. This may be accomplished by, e.g., passingthe laser beam, either from a single chamber laser system or from theoutput of a multi-chamber laser system or from the seed laser in such amulti-chamber laser system before amplification in another chamber ofthe multi-chamber laser system, through an optical arrangement thatsplits the output beam into pulses and daughter pulses and recombinesthe pulses and daughter pulses into a single beam with the pulses anddaughter pulses angularly displaced from each other by a slight amount,e.g., between, e.g., about 50 μRad and 500 μRad and with each of thedaughter pulses having been delayed from the main pulse(s), e.g., by atleast the temporal coherence length and preferably more than thetemporal coherence length.

This may be done in an optical beam delay path having a beam splitter totransmit a main beam and inject a portion of the beam into a delay pathand then recombining the main beam with the delayed beam. In therecombination, the two beams, main and delayed, may be very slightlyangularly offset from each other (pointed differently) in the far field,referred to herein as imparting a pointing chirp. The delay path may beselected to be longer than the temporal coherence length of the pulses.

The angular displacement may be accomplished using a wedge in theoptical delay path prior to the delayed beam returning to the beamsplitter which wedge imparts a slightly different pointing to thedelayed beam (a pointing chirp). The amount of pointing chirp, as notedabove may be, e.g., between about 50 and 500 μRad.

The optical delay paths may comprise two delay paths in series, eachwith a respective beam splitter. In such an event each delay path can bedifferent in length such that there is not created a coherence effectbetween the main and daughter pulses from the respective delay paths Forexample, if the delay in the first delay path is 1 ns the delay in thesecond delay path could be about 3 ns and if the delay in the firstdelay path is 3 ns the delay in the second could be about 4 ns.

The wedges in the two separate delay paths may be arranged generallyorthogonally to each other with respect to the beam profile, such thatthe wedge in the first delay path can serve to reduce coherence(speckle) in one axis and the wedge in the other delay path can reducecoherence (speckle) in the other axis, generally orthogonal to thefirst. Thus, the impact on speckle, e.g., contribution to line edgeroughness (“LER”) and/or line width roughness (“LWR”), e.g., at thewafer in exposure of photoresist in an integrated circuit manufacturingprocess can be reduced along feature dimensions in two different axes onthe wafer.

According to aspects of an embodiment of the subject matter disclosed,with, e.g., a 6 mRad cross of the bowtie in a bowtie ring poweramplification stage, the magnification prisms inside the ring cavity maybe slightly different for the in-going and outgoing beams, and could bearranged so that the beam grows slightly as it travels around the ringor shrinks slightly as it travels around the ring. Alternatively, andpreferably according to aspects of an embodiment of the subject matterdisclosed, a result of breaking the larger beam expansion prism into twoseparate pieces, e.g., enabled by larger spacing between out-going andin-coming beams, e.g., about 5-6 mm, as illustrated by way of example inFIG. 30, applicants propose to adjust the angles of the two prisms,e.g., 146, 148 shown schematically in FIG. 4, such that they result inthe same magnification for both out-going and in-coming beams, e.g.,beams 100 and 62, respectively, shown illustratively and schematicallyin FIG. 30.

According to aspects of an embodiment of the subject matter disclosedapplicants propose to place the Rmax, e.g., 164 and the OC, e.g., 162portions of the version of the seed injection mechanism containing anRmax 164 and an OC 162, e.g., along with the positioning of the systemhorizontal axis beam output aperture on that same stage. This enables,e.g., prior alignment of each as an entire unit and removes the need forfield alignment of the individual components. This can allow, e.g., forthe position of the Rmax/OC assembly, e.g., 160, shown in FIG. 2 (a seedinjection mechanism) to be fixed, just like the OC location in aapplicants' assignee's single chamber oscillator systems (e.g., XLS 7000model laser systems) is fixed. Similarly, such an arrangement can allowfor the achievement of tolerances such that the Rmax/OC are positionedrelative to the system aperture properly without need for significantongoing adjustment. The beam expansion prism may be moveable foralignment of the injection seed mechanism assembly with the chamber 144of the amplification gain medium and the output beam 100 path with thelaser system optical axis.

According to aspects of an embodiment of the subject matter disclosedapplicants propose to position a mechanical shutter to block the MOoutput from entering the ring, when appropriate, similar to such as areutilized on applicants' assignee's OPuSs, e.g., to block them duringalignment and diagnosis. The exact location could be, e.g., just abovethe last folding mirror prior to the ring power amplification stage,where the mini-OPuSes are protected during unseeded ring poweramplification stage alignment and operation.

It will be understood by those skilled in the art that there isdisclosed herein an apparatus and a method for use of a line narrowedpulsed excimer or molecular fluorine gas discharge laser system whichmay comprise a seed laser oscillator producing an output comprising alaser output light beam of pulses comprising: a first gas dischargeexcimer or molecular fluorine laser chamber; a line narrowing modulewithin a first oscillator cavity; a laser amplification stage containingan amplifying gain medium in a second gas discharge excimer or molecularfluorine laser chamber receiving the output of the seed laser oscillatorand amplifying the output of the seed laser oscillator to form a lasersystem output comprising a laser output light beam of pulses, which maycomprise a ring power amplification stage. The ring power amplificationstage may comprise an injection mechanism which may comprise a partiallyreflecting optical element, e.g., a beam splitter, which may be apartially reflective optical element and may be polarization sensitive,through which the seed laser oscillator output light beam is injectedinto the ring power amplification stage. The ring power amplificationstage may comprise a bow-tie loop or a race track loop. The ring poweramplification stage may amplify the output of the seed laser oscillatorcavity to a pulse energy of over 1 mJ, or 2 mJ, or 5 mJ, or 10 mJ or 15mJ. The laser system may operate at, e.g., an output pulse repetitionrate of up to 12 kHz, or ≧2 and ≦8 kHz or ≧4 and ≦6 kHz. The lasersystem may comprise a seed laser oscillator producing an outputcomprising a laser output light beam of pulses which may comprise afirst gas discharge excimer or molecular fluorine laser chamber; a laseramplification stage containing an amplifying gain medium in a second gasdischarge excimer or molecular fluorine laser chamber receiving theoutput of the seed laser oscillator and amplifying the output of theseed laser oscillator to form a laser system output comprising a laseroutput light beam of pulses, which may comprise a ring poweramplification stage. The laser system may operate within a matrix ofoperating values that can serve to optimize laser lifetime and produceother advantageous results including better pulse energy stability andthe like, e.g., the seed laser oscillator containing a lasing gascomprising a mixture of fluorine and other gases and operating at ≦350kPa of total lasing gas pressure, or ≦300 kPa of total lasing gaspressure, or ≦250 kPa of total lasing gas pressure, or ≦200 kPa of totallasing gas pressure or ≧35 kPa of fluorine partial pressure, or ≧30 kPaof fluorine partial pressure, ≧25 kPa of fluorine partial pressure, or≧20 kPa of fluorine partial pressure and combinations of the above. Thesystem may further comprise a coherence busting mechanism intermediatethe seed laser oscillator and the ring power amplification stage. Thecoherence busting mechanism may sufficiently destroy the coherence ofthe output of the seed laser reduce speckle effects in a processing toolusing the light from the laser system. The coherence busting mechanismmay comprise a first axis coherence busing mechanism and a second axiscoherence busing mechanism. The coherence busting mechanism may comprisea beam sweeping mechanism. The beam sweeping mechanism may be driven inone axis by a first time varying actuation signal. The beam sweepingmechanism may be driven in another axis by a second time varyingactuation signal. The first actuation signal may comprise a ramp signaland the second actuation signal may comprise a sinusoid. The timevarying signal(s) may have a frequency such that at least one full cycleoccurs within the time duration of a seed laser output pulse. Thecoherence busting mechanism may comprise an optical delay path withmisaligned optics producing a hall of mirrors effect. The coherencebusting mechanism may comprise an optical delay path longer than thecoherence length of the seed laser output pulse. The coherence bustingmechanism may comprise an active optical coherency busting mechanism anda passive optical coherency busting mechanism. The active coherencebusting mechanism may comprise a beam sweeping device and the passivecoherence busting mechanism may comprise an optical delay path. Thecoherence busting mechanism may comprise a first optical delay path witha delay longer than the coherence length of the seed laser output pulseand a second optical delay path in series with the first optical delaypath and having a delay longer than the coherence length of the seedlaser output pulse. The delay of the second optical delay path may begreater than or equal to about 3 times the coherence length of the seedlaser output pulse. The coherence busting mechanism may comprise a pulsestretcher. The pulse stretcher may comprise a negative imaging opticaldelay path. The pulse stretcher may comprise a six mirror OPuS. Thecoherence busting mechanism may a beam flipping mechanism. The systemand method may comprise the use of a line narrowed pulsed excimer ormolecular fluorine gas discharge laser system which may comprise a seedlaser oscillator producing an output comprising a laser output lightbeam of pulses which may comprise a first gas discharge excimer ormolecular fluorine laser chamber; a line narrowing module within a firstoscillator cavity; a laser amplification stage containing an amplifyinggain medium in a second gas discharge excimer or molecular fluorinelaser chamber receiving the output of the seed laser oscillator andamplifying the output of the seed laser oscillator to form a lasersystem output comprising a laser output light beam of pulses, which maycomprise a ring power amplification stage; a coherence busting mechanismintermediate the seed laser oscillator and the ring power amplificationstage. The ring power amplification stage may comprise an injectionmechanism comprising a partially reflecting optical element throughwhich the seed laser oscillator output light beam is injected into thering power amplification stage. The system and method may comprise theuse of a broad band pulsed excimer or molecular fluorine gas dischargelaser system which may comprise a seed laser oscillator producing anoutput comprising a laser output light beam of pulses which may comprisea first gas discharge excimer or molecular fluorine laser chamber; alaser amplification stage containing an amplifying gain medium in asecond gas discharge excimer or molecular fluorine laser chamberreceiving the output of the seed laser oscillator and amplifying theoutput of the seed laser oscillator to form a laser system outputcomprising a laser output light beam of pulses, which may comprise aring power amplification stage; a coherence busting mechanismintermediate the seed laser oscillator and the ring power amplificationstage. The ring power amplification stage may comprise an injectionmechanism comprising a partially reflecting optical element throughwhich the seed laser oscillator output light beam is injected into thering power amplification stage. The system and method may comprise theuse of a pulsed excimer or molecular fluorine gas discharge laser systemwhich may comprise a seed laser oscillator producing an outputcomprising a laser output light beam of pulses which may comprise afirst gas discharge excimer or molecular fluorine laser chamber; a linenarrowing module within a first oscillator cavity; a laser amplificationstage containing an amplifying gain medium in a second gas dischargeexcimer or molecular fluorine laser chamber receiving the output of theseed laser oscillator and amplifying the output of the seed laseroscillator to form a laser system output comprising a laser output lightbeam of pulses; e.g., a MOPA or MOPO configured dual chamber seedlaser/amplifying laser system, such as applicants' assignee's MOPAXLA-XXX model laser systems, and further comprising a coherence bustingmechanism, of the kind(s) discussed herein, intermediate the seed laseroscillator and the amplifying gain medium stage. The amplification stagemay comprise a laser oscillation cavity. The amplification stagecomprising an optical path defining a fixed number of passes through theamplifying gain medium.

The laser system, e.g., for lithography use may operate within a matrixof MO operating conditions. The ring power amplification stage mayamplify the output of the broad band seed laser oscillator cavity to apulse energy of over 1 mJ, or 2 mJ, or 5 mJ, or 10 mJ or 15 mJ or 20 mJor greater. The laser system may operating at an output pulse repetitionrate of up to 12 kHz, or ≧2 and ≦8 kHz or ≧4 and ≦6 kHz. The system maycomprise the seed laser oscillator containing a lasing gas comprising amixture of fluorine and other gases and operating at ≦500 kPa or ≦400kPa, or ≦350 kPa of total lasing gas pressure, or ≦300 kPa of totallasing gas pressure, or ≦250 kPa of total lasing gas pressure, or ≦200kPa of total lasing gas pressure. The system may comprise ≦50 kPa or ≦40kPa, or ≦35 kPa of fluorine partial pressure, or ≦30 kPa of fluorinepartial pressure, ≦25 kPa of fluorine partial pressure, or ≦20 kPa offluorine partial pressure.

Turning now to FIG. 32 there is shown in schematic form a pulsestretcher 160 a, which can be, e.g., a version of the optical pulsestretcher (“OPuS”) sold with applicants' assignee's laser systemshowever with, e.g., much shortened delay paths not designed for pulsestretching per se, i.e., enough stretching for significant pulseelongation in the spatial and temporal domains, e.g., increasing theT_(is) by 4× or more as in applicants' assignee's currently sold OPuSpulse stretchers. However, the same folding/inverse imaging effects onthe beam for coherency busting purposes, or also as explained in regardto the beam mixer of FIG. 31, can be achieved.

The coherency buster 160 a may have an input beam 162 a incident on abeam splitter 164 a, e.g., a partially reflective mirror 164 a for thepertinent wavelength. Part of the beam 162 a that is reflected into thedelay path comprised of a plurality of mirrors, e.g., confocal mirrors166 a, is imaged back onto the partially reflective mirror 164 a, e.g.,once or multiple times. It will be understood that such opticalcoherence busters may have more than four mirrors, e.g., six mirrors,but are illustrated schematically with only four for convenience andclarity. The delay path may be much shorter than the seven to ten metersor so of, e.g., a 4×OPus, such that the second and third passes throughthe delay path substantially overlap the pulses entering and leaving thecoherency buster 160 a, but do not even substantially stretch thepulses. As will be understood by those skilled in the art, the delaypath may include flat mirrors. Also, the number of curved imagingmirrors may be odd, in which event negative one imaging may occur, oreven, in which plus one imaging may occur.

FIG. 33 shows partly schematically and partly in block diagram form anexample of a coherence busting scheme 360 a and the results of aspectsof the scheme according to aspects of an embodiment of the disclosedsubject matter, e.g., in terms of beam divergence and thus coherencebusting. The illustrated system may incorporate, e.g., anoscillator/amplifier laser 370 a, e.g., including a solid state orexcimer seed laser 372 a, and an oscillator amplifier laser 394 a, orother power amplification stage, e.g., a ring power amplification stage.The amplifier gain medium 394 a may be, e.g., an excimer laser arrangedin a power oscillator configuration, e.g., with a fully reflective rearcavity mirror 396 a and an input/output coupler, e.g., 398 a. It will beunderstood that other seed laser/amplification stage arrangements, someof which are discussed herein, may also be used with the schematicallyillustrated coherence busting scheme shown by way of example in FIG. 33.

At the output of the seed laser 372 a is illustrated a representation ofthe seed laser output laser light pulse beam divergence 374 a containinga single dot indicative of relatively high coherency. The output of theseed laser 372 a may be passed through one or more coherency busters,e.g., 376 a, 378 a, e.g., as shown by example in FIG. 32, or 1050illustrated in FIG. 31 (discussed in more detail in the co-pendingapplication U.S. patent application Ser. No. 10/881,533, filed on Jun.29,2004) or other optical elements such as disclosed in US20050286599,referenced above, or one or more mini-OPuS coherence busting mechanismsdiscussed above, or combinations thereof. A possible embodimentaccording to aspects of an embodiment of the disclosed subject mattermay be the use of a confocal OPuS, e.g., one like that disclosed in theco-pending U.S. patent application Ser. No. 10/847,799, entitled LASEROUTPUT LIGHT PULSE STRETCHER, filed on May 18, 2004, referenced above,with, e.g., two confocal spherical mirrors and four passes of delaypath, i.e., from the beam splitter to mirror No. 1 to mirror No. 2 backto mirror No. 1 and back to mirror No. 2 and then returned to the beamsplitter, passing through, e.g., an offset correction optic, e.g., asdiscussed in the co-pending U.S. patent application Ser. No. 11/394,512,entitled CONFOCAL PULSE STRETCHER, filed on Mar. 31, 2006,referencedabove. This version of a so-called “mini-OpuS” may comprise two pulsestretchers in series, e.g., with a delay path offset selected toslightly shift the high frequency peaks in the temporal pulse intensitycurve of the output of the master oscillator. This may be achieved by,e.g., a delay offset of about 2 ns for a first 1 ns and then three nsdelay line mini-OPuS pair or about a 1 ns delay between a 3 ns and 4 nsdelay line mini-OPuS pair in series or for a 4 ns and 5 ns delay linemini-OPus in series. It will be understood that the pulse itself willnot be stretched significantly, e.g., to come even close to overlapother pulses, but rather will essentially not be stretched at all, sincethe delay path is so much shorter than the ten or so meters of delaypath in the normal pulse stretching OPuSs currently sold by applicants'assignee.

Applicants have noted that producing a 5 ns or greater pulse length froma solid state seed pulse could challenge the present state of the art.However, one can use a mini-OPuS to increase the pulse duration from theseed prior to injection into the amplification stage and this hassuggested to applicants also that one could do this anyway even if onecould produce a longer pulse from the seed. With a shorter pulse fromthe seed and the use 1, 2 or more mini-OPuSs to increase the pulselength, the mini-OPuSs being slightly misaligned would create abroadened divergence prior to injection into the amplification stage.With such a multi-seed mini-OPuS scheme, applicants contemplate thatthere may not be a need for any kind of active beam steering within asingle pulse, especially for non-solid state seed laser systems. One maystill wish to employ active steering for even more smearing of thedivergence, where needed, e.g., in solid state seed laser systems, butit is not contemplated to be necessary in all cases and the seed lasermini-OPuSs need approximately only a 1 foot total path delay, making thebuilding of them right onto the seed laser optical table very straightforward. The stack up of mini-OPuSs and regular OPuSs could look likeFIG. 33, which also shows a cartoon of the divergence as it evolvesthrough the optical train. Assuming a 2.7 multiplication from eachmini-OPuS 376 a, 380 a and a 2.7 multiplication from a misalignedamplifier stage cavity 143 separate “pulses” can be produced. Previousmeasurements with the misaligned amplification stage has indicated toapplicants that there are created 6 independent pulses, so the totalmight be as high as 317. An EO deflector 392 a can easily smear througha pointing space big enough to create at least 4 independent pulses,giving a grand potential total of 1271 pulses. Assuming an initialspeckle contrast of 100%, one could thereby get a speckle contrast of2.8% after all of this bouncing around.

The preferred embodiment uses a first delay something more than 1 ns dueto increased alignment problems with the shorter delay and increasedaberrations in the pulse as stretched in a shorter delay path. Each ofthe delay paths is, however longer than the coherence length of thepulse and the second delay path is longer than the first, to achievecoherence busting effects such as those discussed herein.

The mini-OPuS pulse stretchers may be selected and arranged to, e.g.,fold the beam on itself or fan it out in first one axis, e.g., in afirst mini-OPus 376 a, resulting in the divergence representation 378 aand then in another orthogonally related axis, e.g., in a secondmini-OPuS 380 a, resulting, e.g., in the divergence representation 390a. A pulse steerer 392 a, e.g., and electro-optical (“E-O”) element 392a may sweep (paint) the seed beam into the input/output coupler 400 a ofthe amplifier portion 394 a resulting in the blurring in one axis asshown in the pulse divergence representation out of the power oscillator410 a (and also the divergence representation 410 into the amplificationgain stage 394 a). The “regular” or “standard” OPuS, e.g., a 4×T_(is)OPuS (roughly ten meters of delay path), which may contain, e.g., 2delay paths 412 a, 420 a initiated by a first beam splitter 414 a and asecond beam splitter 422 a, similarly may be arranged to fold the beamon itself in first one axis and then a second resulting, e.g., in thepulse divergence representations of, respectively, 414 a and 424 a. Thefinal divergence representation 424 a shows schematically that thedivergence of the seed beam has been greatly increased, i.e., the beamhas been smeared in its passage from the seed laser 372 a to theamplifier gain medium 394 a and as amplified in the amplifier gainmedium 394 a and subsequently further having its coherency busted in the4× regular OPuS 412 a, 420 a. this increased divergence results inreduced coherence.

It will be understood by those skilled in the art that depending on theinitial coherency of the pulse, e.g., out of the seed laser, e.g.,almost completely coherent in the case of solid state seed lasers tovery little coherency, but still coherency that is desired to be evenfurther reduced, e.g., with an excimer seed laser the type, number andarrangement of coherency busting elements may vary. For example, it mayonly be necessary to do active coherency busting, e.g., with one form oranother of pulse steering/painting, for solid state seed lasers, andthis may in some cases for some applications prove to need only a rampor only AC pulse deflection, i.e., in one axis or the other, or mayprove to need both DC and AC pulse painting (Hybrid painting) along withOPuS effect coherency busting both between the MO and amplifier gainmedium, e.g., PO or PA or other amplification gain medium stage, e.g., aring power amplification stage, and also may need to employ the effectof the regular OPuS pulse stretcher(s) on the output of the amplifiergain medium. With an excimer gas discharge laser MO, with relativelymuch lower coherency than from a solid state seed laser, only passivecoherency busting, e.g., between the MO and gain amplifier medium may beneeded, e.g., with one or both of the mini-OPuSs 376, 380 or otherpassive optical elements as noted above between the MO and amplifiergain medium.

One may still need, however, to do beam steering also, e.g., with anactive beam steering mechanism, such as discussed above, for even moresmearing of the pulse (more divergence), that may be less essential andneed a smaller sweeping angle. Such a seed laser mini-OPuS is believedto need approximately only a 1 foot total path delay each and can alsobe conveniently built onto the seed laser optical table as is currentlythe practice for relay optics in applicants' assignee's XLA series lasersystems.

FIG. 34 illustrates an exemplary relative speckle intensity for a 1 kVE-O deflector voltage v. relative timing The relative standard deviationcurve 550 a is for 1 kV and the equivalent pulse curve is curve 550 a′.A 2 kV E-O deflector voltage curve 552 a and equivalent pulse curve 552a′ are also shown as is a 3 kV E-O deflector voltage curve 554 a andequivalent pulse curve 554 a′. An example of a point shift vs. E-Ovoltage curve 560 a is shown by way of example in FIG. 35. A plot ofpointing shift (inferred by applicants from speckle shift measurements)v. E-O cell applied voltage is shown in FIG. 35. According to aspects ofan embodiment of the disclosed subject matter applicants propose tosweep the pointing of the seed laser within a single pulse in order toreduce the speckle contrast within. This may be done, e.g., with electrooptical elements, e.g., elements 1912 and 1914 shown illustratively inthe schematic and partly block diagram illustration of aspects of anembodiment of the disclosed subject matter found in FIG. 66. Usingvertical expansion prior to input of a seed laser pulse into an excimerpower oscillator, e.g., a XeF chamber, placed as close to an inputcoupler, e.g., a beam splitter, and with a clear aperture of the E-Odeflector at around 3.2 mm in diameter, the deflector may have to beupstream of the vertical expansion (not shown in FIG. 66). To minimizeany translation in the oscillator cavity, e.g., the XeF cavity 1930,e.g., associated with the angular tilt from the E-O deflector, it may bedesirable to place the E-O deflector as close to the amplifier cavity aspossible.

According to aspects of an embodiment of the disclosed subject matter itis contemplated to apply a time changing voltage on a timescale similarto the seed pulse duration, e.g., by applying a DC voltage level untiltriggered, at which point the high voltage may be shorted to ground,e.g., via a stack of fast MOSFETS, e.g., illustrated schematically inFIG. 45 as a single transistor 1130 a. A plot of the applied voltage andthe seed laser pulse shape are shown in FIG. 36. Placing a seriesresister between the E-O cell terminal and voltage supply can be used tocontrol, e.g., the voltage slope applied to the E-O cell. The 50 pFcapacitance of the E-O cell in series with, e.g., a 200Ω resister givesan initial slope of about 10¹¹ λrad's. The voltage across the E-O celldrops, e.g., as seen in FIG. 36 from the DC level to nearly zero in atime similar to the seed pulse duration. By changing the relative timingbetween the E-O cell pulser and the seed laser one can, e.g., change theamount of pointing sweep that occurs during the seed pulse. In addition,one can change the value of the initial DC voltage to effect a greateror lesser pointing sweep during the seed pulse. Applicants have testedthis fast pointing capability, e.g., with the seed laser only andreflecting from an OC only, therefore, with no OPuS effect from themultiple reflections from the OC and Rmax and no effects due to MOPOoperation. Without optimizing for relative timing between the E-O celland the seed pulse, applicants captured speckle patterns for a range oftiming between the two. Applicants applied three difference levels of DCvoltage to the E-O cell in order to change the maximum availablepointing slope. The results showed a minimum speckle intensitynormalized standard deviation at about 57 ns relative timing as seen,e.g., in FIG. 34. Without any angular shift during the seed pulse, atboth small and large relative timing values, below and above 57 ns thespeckle contrast is high. This correlates with values found byapplicants during static testing. When, e.g., the relative timing placesthe E-O Cell voltage slope coincident with the seed pulse, the specklepattern of a single pulse is smeared in the vertical direction, in adramatic and satisfactory way.

One can normalize these contrast values to the maximum value in order toevaluate the percentage reduction in contrast, e.g., brought about bythe dynamic pointing shift. At the optimum relative timing point thespeckle contrast was found to be reduced to about 40% of its peak. Usingthe 1/√{square root over (N)} assumption for equivalent number ofindependent pulses the data can be used to derive the number of pulsesrequired to achieve this level of speckle contrast reduction. At theoptimum relative timing, and with 3 kV applied to the E-O cell, thecontrast reduction was found to be equivalent to 6 pulses. Even highervoltage levels (and thus even larger pointing shift during a singlepulse) could improve this result. Applicants performed similarmeasurements with the seed laser pulse entering the MOPO amplificationstage cavity, but no discharges between the AMPLIFICATION STAGEelectrodes and noted that reflections from the OC and the Rmax in theXeF cavity, from the OPuS effect, beam spreading alone, indicated thatthe maximum speckle contrast was reduced by the amount predicted by theOPuS effect (N=1.56 with a 20% OC, giving 1/√{square root over(n)}=0.80. Thus 70% contrast becomes 56%). The effect of smearing, eventhough the initial speckle contrast is lower, appears not to change whenadding the secondary reflections from the full XeF cavity. Theequivalent pulse for speckle reduction is still about 6.

Applicants performed similar measurements with AMPLIFICATION STAGEcavity electrodes discharging and thus implicating the effects of theamplification within the AMPLIFICATION STAGE cavity, which indicated asshown in FIG. 34 the decrease in the impact on speckle reduction throughseed beam sweeping. With such a configuration, the effect was found tobe just over half of the equivalent number of pulses produced, i.e.,about 3, when operating as a MOPO, also found was a rather largereduction in peak speckle contrast, with no smearing. Previousmeasurements of MOPO operation showed a reduction equivalent to about 6pulses. These results show a reduction equivalent to about 8 pulses.Applicants suspect that the AMPLIFICATION STAGE cavity may discriminateagainst off-axis ray angles, e.g., in a flat-flat cavity, and thus thespray of angles sent into the cavity may not all be equally amplified(this could be corrected, e.g., with a true stable cavity, e.g.,employing a curved OC and a curved Rmax). Another explanation may bethat not all of the seed pulse takes part in controlling theAMPLIFICATION STAGE characteristics. Maybe only, e.g., the first 5 ns ofthe seed pulse's 10-15 ns pulse duration controls the AMPLIFICATIONSTAGE and thus the E-O sweep is not fast enough to occur within thatsmaller window. This may also be corrected, e.g., by using a smallerresister and a shorter sweep.

According to aspects of an embodiment of the disclosed subject matterapplicants propose to use a 6 mirror coherency busting mechanism (forconvenience herein optical pulse delay paths are indicated schematicallyas having four mirrors per delay path) which has been developed byapplicants' assignee for additional path delay inside either or both ofthe 1^(st) or 2^(nd) pulse stretchers in the OPuS used with applicants'assignee's XLA model multi-chamber laser systems. Such a delay path can,e.g., produce −1 imaging for each sub-pulse. This is illustratedschematically and in cartoon fashion, e.g., in FIG. 37 wherein isillustrated the summation of these “flipped” sub-pulses. The flippedsub-pulses shown, e.g., in FIG. 8 can be used, e.g., for improvedprofile uniformity and symmetry. A 6 mirror design can convert pointingshifts into a divergence increase which may, e.g., be beneficial in aring arrangement for ASE reduction. The standard 4 mirror design doesnot. It will be understood that the delay path for this coherencybusting purpose need not be as long as the actual OPuS used for pulsestretching to get a much increased pulse T_(is), e.g., forphotolithography uses. Rather the coherency busting mechanism, aso-called “mini-OPuS”, just needs to fold the pulses a certain number oftimes. This is illustrated by the pulse 580 a, with the corner(pre-flip) designated 582 a and the pulses 584 a, 586 a, 588 a. Inaddition, due to the almost inevitable misalignment of mirrors in thedelay path, a “hall of mirrors” or so-called OPuS effect, may alsoreduce the coherency in the seed laser pulse, and, e.g., so long as thedelay path exceeds the spatial coherency length of the beam furthercoherency busing occurs in the delay path. In this regard, a four mirrormini-OPuS, e.g., with confocal spherical mirrors for ease of alignment,may serve as a satisfactory coherency buster, even without beam flippingin both axis.

According to aspects of an embodiment of the disclosed subject matter itmay be necessary to combine two separate laser beams at various pointswithin a system according to aspects of an embodiment of the disclosedsubject matter. If only half of the entrance to a 6 mirror pulsestretcher is illuminated, the sub-pulses flip between top and bottom asshown, e.g., in FIG. 8. The summation of these “flipped” sub-pulses canlead to a filled in, full size profile, e.g., as illustrated in thepulse flipping simulation shown in FIG. 41, with the curve 562 a showingthe pulse before entering the delay path and curve 564 a (black) afterone delay path and 566 a (red) after a second delay path. Laserdivergence may then be used to fill in the center portion 568 a, e.g.,after some propagation, e.g., over about 1 m or so.

Use of a solid state laser source for lithography has been proposed inthe past and not pursued for two reasons. Solid state lasers are notconsidered capable of the high average power required for lithographyand a solid state laser produces single mode output which is highly(perfectly) coherent. According to aspects of an embodiment of thedisclosed subject matter applicants propose to address the low averagepower problem with, e.g., a hybrid solid state seed/excimer amplifiercombination. The high coherence properties of the solid state seed canbe addressed in a number of ways according to aspects of embodiments ofthe disclosed subject matter, e.g., by creating sub-pulses, e.g., thatare separated in time longer than the coherence length, or by, e.g.,changing the seed laser pointing, e.g., over very short time scales,e.g., within a single laser pulse, or a combination of both. Coherencybusting has been found by applicants to be of benefit in dual chambergas discharge (e.g. excimer) seed/gas discharge (e.g., excimer)amplifier portion lasers as well.

De-phasing of a speckle pattern can be seen from a diffuser 670 a tooccur with a λ/2d where d is the illumination width for a slot apertureand diameter for a circular aperture, e.g., as illustrated schematicallyand in cartoon fashion in FIG. 38. Incoherence of a speckle pattern canalso be seen to occur from each sub-pulse produced by a pulse stretcher,provided that the pulse stretcher delays each pulse by greater than thetemporal length, which can, e.g., be further exploited by, e.g.,intentionally misaligning each pulse stretcher, e.g., a mirror(s) in thepulse stretcher, by a very slight amount. In point of fact, applicants'employer has discovered by testing that it is very hard to preciselyalign the mirrors in, e.g., an 4×T_(is) OPuS type of pulse stretcher,and they are slightly out of alignment almost all the time, withouthaving to intentionally misalign them. This amount of “ordinary”misalignment has been found by applicants employer to be an amountsufficient to achieve a desired level of speckle reduction and isillustrated schematically in FIG. 40, as discussed elsewhere.

The effective number of equivalent independent laser pulses can be seento be equal to the time integral squared (“T_(is)”) magnification of theeach pulse stretcher. Each OPUS pulse stretcher of the kind noted abovemay have a multiplication of around ˜2.4×. With, e.g., three stages ofpulse stretching, the number of independent sub-pulses will be(2.4)³=13.8. Since speckle contrast scales with the number ofindependent sub-pulses, N, as 1/√N, pulse stretchers can provide anoutput speckle contrast of 1√13.8=26.9% with an input speckle contrastof 100%. Since this may still be too high a speckle contrast, accordingto aspects of an embodiment of the disclosed subject matter amechanism(s) may be provided to reduce the speckle contrast into or outof the pulse stretcher(s). The same can be said for the so-calledmini-OPuSs discussed elsewhere.

Electro-optics or acousto-optics can be used for beam steering, e.g.,steering a seed laser light pulse beam within a single pulse in thebeam. Utilization of such, e.g., at the output of the seed laser, canresult in, e.g., according to aspects of an embodiment of the disclosedsubject matter, the electro-optic material(s) only needing to be subjectto a low average power seed laser beam. By, e.g., randomly and/orcontinuously changing the beam steering, e.g., within a single laserpulse, the angular acceptance of the power amplification stage can be“painted” or filled in for each laser pulse. As a result, a main pulsecan have a divergence set, e.g., by the MO/power amplification stageoptical configuration and not, e.g., by the seed laser characteristics.A greatly reduced coherence for the laser system output laser lightpulse can be the result.

According to aspects of an embodiment of the disclosed subject matter aninjection controlled amplifier laser system, e.g., with a plane cavityand flat rear mirror, may have suitable energy stability, e.g., for seedpulse inject energies in the range of 0.0085 to 0.99 mJ. This energy ofthe beam may be, e.g., incident on the rear mirror of, e.g., a poweramplification stage, which may form the input coupler from the seedlaser. This reflector may have, e.g., about a 90% reflection and about8% transmission. Therefore, the seeding energy entering theamplification stage cavity itself may be, e.g., about an order ofmagnitude smaller than what is incident onto the back reflector. With aring cavity, especially with a partially reflecting seed injectionmechanism according to aspects of an embodiment of the disclosed subjectmatter, discussed elsewhere herein, e.g., the input seed energy may bemuch less wasted, e.g., admitting around 80% of the seed laser light. AnRmax and OC can be in an F₂ containing environment, and thus morerobust, though, e.g., if polarization coupling is used, couplingefficiency may still be less than optimum for certain applications. Asuitable architecture, e.g., in a MOPA configuration may be a 2-channel(“tic-toc”) solid state seed laser, e.g., a 3^(rd) harmonic Nd:YLF MO orNd:YAG system (tuned, e.g., to 351 nm) along with a pair of two 3-passXeF PA modules. Such a system in a MOPO, e.g., a master oscillator/poweramplification stage (such as a ring power oscillator amplificationstage) configuration is also considered as an effective alternative.Such a two channel MOPO approach may be similar to the MOPAconfiguration, i.e., with two seeded power oscillators. Various couplingtechniques could be used, e.g., MO coupling using a polarizationtechnique or a seed inject mechanism. Efficiency v. E_(mo) for differingPO/PA configurations has been found to be better for a MOPO or a threepass MOPA, though four pass MOPAs were not tested. Exemplary pulse width(FWHM) has been found to be for an MOPO about 17.3 ns, for a MOPA,single pass, about 13.9 ns and for a MOPA triple pass about 12.7 ns.

Applicants have examined speckle patters for decorrelation with angularshift, e.g., in a MOPO output beam, e.g., with a Nd-YLF seed laser and aXeF power oscillator (e.g., a flat-flat polarization coupledarrangement). With the relative timing between the XeF discharge and theseed laser pulse adjusted and angular and spatial adjustment also madefor maximum suppression of the weak line (353) produced by the XeF gain.

FIG. 39 illustrates schematically the results of a coherency bustingscheme on an output laser pulse, e.g., in relation to a scanner angularacceptance window, e.g., introducing horizontal and vertical (asillustrated in the plane of the page drawing of FIG. 39) directions. Thedot 780 a illustrated schematically and by way of example an initialseed laser output pulse divergence profile 780 a. The pattern of pulses782 a illustrate a pattern of sub-pulse divergence profiles 782 a afterbeam folding in a perfectly aligned beam delay path, or through amisaligned beam delay path or both, or a combination thereof, and thecircles 784 a around each represent the effect on the divergence profileof electro-optical smearing.

Turning now to FIG. 40 there is shown a schematic representation of theeffects of coherence busting according to aspects of an embodiment ofthe disclosed subject matter. Utilizing an imaging delay path, e.g., apulse stretcher, e.g., a so-called optical pulse stretcher (“OPuS”),e.g., a 4×T_(is) six mirror OPuS sold with the above noted applicants'assignee's laser systems, and illustrated in United States Patents andco-pending applications noted above, or a modified version thereof witha shorter delay path used, e.g., for folding the beam on itself and/orfor delay exceeding the coherence length as discussed above, theso-called mini-OPuS, one can achieve a degree of coherence busting,e.g., between the MO and amplifier gain medium, e.g., a PA or a PO or aring power amplification stage. Other forms of coherence busting e.g.,as illustrated in FIG. 31 could be used alone or in combination withsuch a “mini-OPuS,” e.g., as illustrated in FIG. 33 and elsewhereherein.

According to aspects of an embodiment of the disclosed subject matter,the pointing/divergence sensitivity of a pulse stretcher, e.g., a 4mirror 6 mirror pulse stretcher, e.g., a regular OPuS such as a 4×T_(is)OPuS, or a so-called mini-OPuS, or the delay path discussed in moredetail in regard to FIG. 31, can be put to advantage, e.g., by addingactive mirror control with feedback from, e.g., a pointing/divergencesensor, illustrated, e.g., in FIGS. 13, 14 and 42. Such advantagesinclude creating, e.g., a hall of mirrors effect whereby, e.g., thelaser output light pulse beam being smoothed in the delay path and,further, actually becomes something like a plurality of beams of veryslightly different pointing and thus angles of incidence on the variousmirrors of the pulse stretcher. Applicants assignee has observed this inpulse stretchers where it is very difficult to perfectly align themirrors, e.g., of the currently used 4×T_(is) OPuS pulse stretcher, thuscreating the hall of mirrors effect that reduces the coherence of thelaser output light pulse beam exiting the pulse stretcher. Thus the beam860 a forms a plurality of separate beams 82 a. In FIG. 40 this is alsoillustrated schematically and as a result of a flat-flat cavity 850 awith slightly misaligned mirrors forming the rear of the cavity 852 aand an output coupler 854 a, but the same effect has been observed in anOPuS by applicants employer with the coherence busting effect notedabove. The cavity illustrated in FIG. 40 may also have a polarizinginput coupler 858 a and a quarter wave plate 856 a.

FIG. 40 illustrates a reduction in coherency, e.g., when using both thereflectivity of an OC and an Rmax, e.g., in a flat-flat cavity with,e.g., a polarizing input coupling from a seed laser source of seed laserpulses. The angles have been exaggerated for clarity of illustration.There are, e.g., multiple rays produced by a static fan out, i.e., “hallof mirrors” effect, e.g., created between the OC and the Rmax. Thetheoretical energy weighting of these rays, assuming no transmissionlosses through the cavity and perfect reflectivity is shown below.

Ray Normalized Number Fractional Energy Energy 1 0.2 = 0.200 0.3125 20.8 * 0.8 = 0.640 1.000 3 0.8 * 0.2 * 0.8 = 0.128 0.2000 4 0.8 * 0.2 *0.2 * 0.8 = 0.0256 0.0400 5 0.8 * 0.2 * 0.2 * 0.2 * 0.8 = 0.00512 0.00806 0.8 * 0.2 * 0.2 * 0.2 * 0.2 * 0.8 = 0.00102 0.0016One may assume that each ray is incoherent from all others, e.g., wherethe path length between the OC and the Rmax is maintained to be longerthan the temporal coherence length. Each ray may also be assumed, e.g.,to be angled slightly different from all others since, e.g., perfectalignment is believed to be extremely difficult, especially in thevertical direction. Applicants believe that about 37 μrad of angledifference in the vertical direction is needed to create uncorrelatedspeckle. Summing the normalized energy weighting to give the equivalentnumber of independent pulses and taking the square root to give thereduction in standard deviation, the sum from the above is 1.56. Thesquare root is 1.25 and thus the standard deviation when using both OCand Rmax reflections is predicted to be 0.551/1.25=0.440, which compareswell with a value that applicants have measured, i.e., 0.427.

Static fan out, otherwise referred to herein as a hall of mirrorseffect, believed to be essentially unavoidable with manual alignment,produces a single pulse speckle contrast with amplification in anamplification gain medium that is 2.50× smaller than the seed laseralone. This reduction is the equivalent of 6.3 uncorrelated sub-pulses.Some of this contrast reduction is due to the weak line content from theXeF power oscillator used for testing the effects of the oscillationamplification stage, but most is believed to be due to the static fanout effect. Likely, many of the sub-pulses created by the OPuS-likestatic fan out characteristics of the OC-Rmax (OC-rear cavity mirror)reflections are all amplified to nearly equal intensities and thuscreate more equivalent independent pulses than shown in the above table.

Tilt angle required to produce uncorrelated speckle patterns may besignificant. The first big jump in equivalent pulses, from 1.0 to 1.55,is believed by applicants to be mostly due to the poor pulse-to-pulserepeatability of the speckle patterns when running as a MOPO. Evenwithout changing the mirror tilt at all, two pulses are correlated nobetter than 30-35%. With seed only, this pulse-to-pulse correlation hasbeen found to be about 85-90%. The long slow rise in equivalent pulsenumber does not even reach a value of 2.0 until about 400 μrad of mirrortilt as illustrated, e.g., in FIG. 46. This result could mean, e.g.,there may be a need for a large angular sweep, of about ±500-1000 μrad,e.g., to create several uncorrelated speckle patterns in a single pulse.

Through experimentation relating to coherence applicants' employer haslearned that, e.g., sub-pulses produced by a pulse stretcher areincoherent and lead to a different fringe pattern if their angles areslightly shifted. The pin hole fringe pattern shifts maximum to minimumwhen input angle is λ/2d.

A plot of pointing shift (inferred by applicants from speckle shiftmeasurements) v. E-O cell applied voltage is shown in FIG. 35. Accordingto aspects of an embodiment of the disclosed subject matter applicantspropose to sweep the pointing of the seed laser within a single pulse inorder to reduce the speckle contrast within. This may be done, e.g.,with electro optical elements, e.g., element 392 a illustratedschematically in FIG. 33. Using vertical expansion prior to input of aseed laser pulse into an excimer power oscillator, e.g., a XeF chamber,placed as close to an input coupler, e.g., a beam splitter, and with aclear aperture of the E-O deflector at around 3.2 mm in diameter, thedeflector may have to be upstream of the vertical expansion (not shownin FIG. 33). To minimize any translation in the oscillator cavity, e.g.,associated with the angular tilt from the E-O deflector, it may bedesirable to place the E-O deflector as close to the amplifier cavity aspossible.

Turning now to FIG. 42 there is shown schematically and partly in blockdiagram form a beam combiner system 600 a, according to aspects of anembodiment of the disclosed subject matter. The beam combiner system 600a may include, e.g., a first amplifier gain medium portion 602 a and asecond amplifier gain medium portion 604 a, each of which may be, e.g.,a PA or PO or ring power amplification stage, as described elsewhere inthe present application. The output of each of the amplifier portions602 a, 604 a may pass through a beam expander 608 a, which may include aprism 610 a and a prism 612 a, e.g., magnifying the beam by 4×. Aturning mirror 620 a may steer a first laser system output light pulsebeam 622 a from the amplifier 602 a to a second turning mirror 624 awhich may steer the pulse beam 622 a to form a pulse beam 632 a onto abeam splitter for a first pulse stretcher 640 a and thence to a beamsplitter 646 a for a second pulse stretcher 644 a. A turning mirror 630a may steer a second laser system output light pulse beam 632 a from thesecond amplifier 604 a to a second turning mirror 634 a, which may steerthe beam 632 a to form a beam 634 a to be incident on the beam splitter642 a and thence the beam splitter 646 a. The output of the first OPuSand second OPuS, which may be “mini-OPuSs” as discussed elsewhere in thepresent application, may pass through another beam splitter 650 a,where, e.g., a small portion of the laser system output laser lightpulse beam may be diverted, e.g., for metrology purposes, e.g., focusedby a focusing lens 652 a into a divergence detector 654 a, which may bepart of a control system (not shown) providing feedback control signals656 a, e.g., to the beam splitters 642 a, 646 a of the first and/orsecond OPuSs 640 a, 644 a or the turning mirrors for each of the beams632 a, 634 a to increase or decrease divergence. Such coherency bustingmay be at the input to the amplifiers 602 a, 604 a, e.g., shown in FIG.42 as opposed to the outputs.

The effective number of equivalent independent laser pulses can be seento be equal to the T_(is) magnification of the each pulse stretcher.Each OPUS pulse stretcher of the kind noted above may have amultiplication of around ˜2.4×. With, e.g., three stages of pulsestretching, the number of independent sub-pulses will be (2.4)³=13.8.Since speckle contrast scales with the number of independent sub-pulses,N, as 1/√N, pulse stretchers can provide an output speckle contrast of1√13.8=26.9% with an input speckle contrast of 100%. Since this maystill be too high a speckle contrast, according to aspects of anembodiment of the disclosed subject matter a mechanism(s) may beprovided to reduce the speckle contrast into or out of the pulsestretcher(s). The same can be said for the so-called mini-OPuSsdiscussed elsewhere.

Pulse trimming has been demonstrated, e.g., with the utilization ofelectro-optics, e.g., at 193 nm. Rather than polarization rotation, usedin some other forms of pulse trimming, electro-optics can be used forbeam steering, e.g., steering a seed laser light pulse beam within asingle pulse in the beam. Utilization of such, e.g., at the output ofthe seed laser, can result in, e.g., according to aspects of anembodiment of the disclosed subject matter, the electro-opticmaterial(s) only needing to be subject to a low average power seed laserbeam. By, e.g., randomly and/or continuously changing the beam steering,e.g., within a single laser pulse, the angular acceptance of the poweramplification stage can be “painted” or filled in for each laser pulse.As a result, a main pulse can have a divergence set, e.g., by thePO/power amplification stage optical configuration and not, e.g., by theseed laser characteristics. A greatly reduced coherence for the lasersystem output laser light pulse can be the result.

According to aspects of an embodiment of the disclosed subject matter aninjection controlled amplifier laser system, e.g., with a plane cavityand flat rear mirror, may have suitable energy stability, e.g., for seedpulse inject energies in the range of 0.0085 to 0.99 mJ. This energy ofthe beam may be, e.g., incident on the rear mirror of, e.g., a poweramplification stage, which may form the input coupler from the seedlaser. This reflector may have, e.g., about a 90% reflection and about10% transmission. Therefore, the seeding energy entering theamplification stage cavity itself may be, e.g., about an order ofmagnitude smaller than what is incident onto the back reflector. With aring cavity, especially with a partially reflecting seed injectionmechanism according to aspects of an embodiment of the disclosed subjectmatter, discussed elsewhere herein, e.g., the input seed energy may bemuch less wasted, e.g., about 80% is injected to the amplificationstage. An Rmax and OC can be in an F₂ containing environment, and thusmore robust, though, e.g., if polarization coupling is used, couplingefficiency may still be less than optimum for certain applications. Asuitable architecture, e.g., in a MOPA configuration may be a 2-channel(“tic-toc”) solid state seed laser, e.g., a 3^(rd) harmonic Nd:YLF MO orNd:YAG system (tuned, e.g., to 351 nm) along with a pair of two 3-passXeF PA modules. Such a system in a MOPO, e.g., a master oscillator/poweramplification stage (such as a ring power oscillator amplificationstage) configuration is also considered as an effective alternative.Such a two channel MOPO approach may be similar to the MOPAconfiguration, i.e., with two seeded power oscillators. Various couplingtechniques could be used, e.g., MO coupling using a polarizationtechnique or a seed inject mechanism. Efficiency v. E_(mo) for differingPO/PA configurations has been found to be better for a MOPO or a threepass MOPA, though four pass MOPAs were not tested. Exemplary pulse width(FWHM) has been found to be for an MOPO about 17.3 ns, for a MOPA,single pass, about 13.9 ns and for a MOPA triple pass about 12.7 ns.

Applicants have examined speckle patterns for decorrelation with angularshift, e.g., in a MOPO output beam, e.g., with a Nd-YLF seed laser and aXeF power oscillator (e.g., a flat-flat polarization coupledarrangement). With the relative timing between the XeF discharge and theseed laser pulse adjusted and angular and spatial adjustment also madefor maximum suppression of the weak line (353) produced by the XeF gain.

The maximum intensity of the seed pulse has been observed to occurduring the initial, very low level, fluorescence of the amplificationstage. This very low level fluorescence (and thus gain) is believed tobe enhanced by this seed light, as observed in MOPO output. Adjustmentof the timing of the seed earlier than or later than, e.g., about 20 orso ns before the amplification stage firing can, e.g., lead to anincrease in weak line output.

According to aspects of an embodiment of the disclosed subject mattercoherence busting may be accomplished by beam steering, e.g., withelectro-optical elements, e.g., pointing of the seed beam during asingle pulse using, e.g., a ConOptics E-O deflector assembly matched forthe desired nominal center wavelength. Such E-O devices may be likethose used in CD and DVD writers that use a doubled Ar-ion line near 351nm having E-O deflectors used to modulate the beam. With a pointingcoefficient of, e.g., about 0.6 μrad/volt and with a capacitance of 50pF, even a full mrad of deflection requires only 1,700V. A drive circuituseful for pulse trimming, e.g., as illustrated schematically in FIG. 40(discussed in more detail elsewhere in the present application) can beused, e.g., with a resister in series to produce a controlled sweeprate, e.g., during a single pulse. The seed pulse duration can be around15 ns, so the rate of rise is well within the capabilities of such adriver, for reasonable pointing changes, such as up to a mRad. With apumping diode current of around 30 A and 4 A to the oscillator pumpdiode, the seed laser output laser light pulse beam pulse energy wasdetermined to be 1.2 mJ, sufficient for seeding a gas discharge laser,e.g., a XeF gas discharge laser.

A plot of speckle contrast (average speckle cross-correlation versusmirror tilt—input angle change) for a MOPO configuration is shown by wayof example in FIG. 75. A similar plot for only a seed laser pulsepassing through an amplifier gain medium in an oscillator configuration,but without excitation of the amplifier gain medium is illustrated byway of example as plot 590 in FIG. 46, which also shows by way ofexample a plot 592 of equivalent independent pulses. A similar plot isshown in FIG. 74, for the seed laser pulse only in the PO, with curve596 being the equivalent independent pulses, curve 594 being thenormalized standard deviation and curve 598 being the cross correlation.Similar to the MOPO case, it takes about 150-250 μrad of tilt to producecompletely or essentially completely uncorrelated speckle patterns andabout two equivalent independent pulses. But, as described above, thestarting speckle contrast for no shift may be smaller than with the OCreflection only by a factor of about 1.25. Thus according to aspects ofan embodiment of the disclosed subject matter applicants have discoveredthat, e.g., a MOPO single pulse speckle contrast may be significantlylower than a seed-only case, because, e.g., static fan out of the raysproduced by the multiple OC-Rmax-OC-Rmax reflections, e.g., because eachof these reflections exit at the illustrated separate slightly differentangle, producing uncorrelated speckle patterns as shown by way ofexample in FIG. 75.

According to aspects of an embodiment of the present applicationapplicants believe that this discovery may be utilized to greatlysimplify the necessary coherence busting scheme, where a lesser degreeof coherency busting may be found to be necessary. Instead of creatingthe electro-optic capability of, e.g., steering and/or more rapidlymodulating (“hybrid painting,” in the case of using both), e.g., theentire divergence space, e.g., in one or both axes (e.g., requiring highfrequency devices), one can slightly misalign the seed to the PO, e.g.,in one axis or the other or both, to exploit this spreading static rayout effect, the so-called hall of mirrors effect. It may then also bepossible to use, e.g., only a linear sweep of pointing along one axis orthe other or both, e.g., where the one axis is the other axis in thecase of spreading only in one axis, with, e.g., a greatly reducedrequirements on the E-O drive electronics. In the simplest case,misalignment spreading (beam fan-out so-called hall of mirrors effect,may be employed in only one axis and “singly painting” in the other,e.g., with a saw tooth signed to a tilt mirror and without AC creatinghybrid painting. More complex permutations and combinations of thesecoherency busting techniques may also be applicable.

FIG. 43 gives an example of an idealized high frequency painting E-Ovoltage signal superimposed on a ramped (time varying) E-O DC voltagesignal in relation to the intensity of the seed pulse being “painted”,e.g., into a delay path or into the amplifying gain medium, e.g., a PAor PO or other power amplification stage. The ramp voltage may becreated, e.g., by a fast R-C decay of an E-O cell capacitance asillustrated schematically in the circuit of FIG. 45. Due to certainconstraints on a test circuit that applicants have so far built andtested, e.g., limited RF frequency, impedance mismatch, E-O load cellcapacitance mismatch and the like, the actual voltages delivered by the“painting” circuit are shown in FIG. 44, as best as could be measuredconsidering difficulties with probe loading, etc. These areapproximately 25% of the needed RF frequency (e.g., about 100 MHz asopposed to 400 MHz) and 10% of the needed peak to peak voltage (e.g.,around ±200 kV as opposed to ±2000 kV). The painting voltages could, ofcourse, be better optimized, however, the test circuit was used todemonstrate the effectiveness of “painting” the seed beam into theamplifier gain medium for coherency/speckle reduction, e.g., with hybridpainting using both time varying DC steering and AC modulation, e.g.,one in one axis and the other in a second axis, e.g., orthogonallyrelated to each other.

Applicants' experimental measurements have determined that with no rampand no AC voltage the 2D speckle contrast overall is 76.8% and variesfrom the horizontal to the vertical axis. With painting using the rampalone the speckle contrast overall was 29.4%, again varying in the twoaxes. Painting with the AC alone gave a speckle contrast overall of59.9%, again varying in the two axes. With the ramp and AC voltagesapplied the spectral contrast was 28.1% overall and varying in bothaxes. This was using a less optimized circuit than the one of FIG. 40,which was not available for the testing and the actual tested circuittest results are shown in FIG. 44.

Applicants believe that a more optimized circuit, shown by way ofexample in FIG. 45, will even improve further the reduction in specklecontrast. The circuit 1100 a of FIG. 40 may include, e.g., an E-O cell,such as noted above, with an E-O cell capacitance 1104 a and animpedance matching inductor 1110 a, and an N:1 step-up transformer 1120a. Also included as illustrated may be, e.g., a DC power supply 1122 acharging a capacitor 1126 a through a large resistor 1130 a and an RFfrequency generator connected to a fast acting switch, e.g., atransistor 1140 a (in reality a bank of such transistors in parallel),through a resistor. Also the capacitor 1126 a discharges through a smallresistor 1142 a when the switch 1140 a is closed.

According to aspects of an embodiment of the disclosed subject matter“painting” may also be done upstream of the amplifier gain medium, e.g.,by tilting a mirror upstream of the amplification, e.g. apiezo-electrically adjustable mirror, if paining need not be done withina pulse time, or a piezo-drive fast enough for such painting is orbecomes available, and otherwise with, e.g. a electro-optical oracousto-optical beam deflector. The results with the seed only, bothwith OC only and with OC plus Rmax reflections, look very similar tothose measured by applicants such as with tilting a mirror, e.g.,through a diffuser as illustrated in FIG. 22. As with the previousmeasurements, the OPuS-like characteristics of the OC-Rmax reflectionscan be seen to lead to single-pulse speckle contrast values reduced bythe equivalent number of sub-pulses produced. The angular tilt requiredto produce uncorrelated speckle patterns was determined to be about200-250 μrad, again similar to the results with tilting the mirror,e.g., downstream from the power amplification stage.

Applicants have performed characterizations of a solid state MO./poweramplification stage using an excimer seed laser, e.g., greatlyattenuated to simulate the expected pulse energy of, e.g., a 193 nmsolid state laser. The pulse duration produced, however, did not matchthat expected from a 193 nm solid state laser. Applicants believe thatproper simulation of the seed pulse duration should further reduce thetotal seed laser energy required for MO/power amplification stageoperation. Using a pulse trimmer, e.g., a Pockels cell to which wasapplied a step voltage, e.g., timed to trim the later portion of theexcimer seed pulse shape (¼λ voltage=2.5 kV), and due to the rise timeof the excimer seed laser pulse and the fall time of the Pockels cell,the shortest practical pulse shape attained was about 9 ns FWHM and ˜15ns foot-to-foot. Trimming the later portion of the seed pulse wasdetermined to have virtually no impact on the MO/power amplificationstage output pulse characteristics, e.g., intensity, even withapproximately 25% of the seed pulse energy eliminated. However, as notedelsewhere in the present application pulse trimming may further reducespeckle by eliminating a portion(s) of the output pulse with thegreatest coherency (least speckle contrast).

According to aspects of an embodiment of the disclosed subject matter itis contemplated to apply a time changing voltage on a timescale similarto the seed pulse duration, e.g., by applying a DC voltage level untiltriggered, at which point the high voltage may be shorted to ground,e.g., via a stack of fast MOSFETS, e.g., illustrated schematically inFIG. 40 as a single transistor 1130. A plot of the applied voltage andthe seed laser pulse shape are shown in FIG. 19. Placing a seriesresister between the E-O cell terminal and voltage supply can be used tocontrol, e.g., the voltage slope applied to the E-O cell. The 50 pFcapacitance of the E-O cell in series with, e.g., a 200Ω resister givesan initial slope of about 10¹¹ μrad/s. The voltage across the E-O celldrops, e.g., as seen in FIG. 19 from the DC level to nearly zero in atime similar to the seed pulse duration. By changing the relative timingbetween the E-O cell pulser and the seed laser one can, e.g., change theamount of pointing sweep that occurs during the seed pulse. In addition,one can change the value of the initial DC voltage to effect a greateror lesser pointing sweep during the seed pulse. Applicants have testedthis fast pointing capability, e.g., with the seed laser only andreflecting from an OC only, therefore, with no OPuS effect from themultiple reflections from the OC and Rmax and no effects due to MOPOoperation. Without optimizing for relative timing between the E-O celland the seed pulse, applicants captured speckle patterns for a range oftiming between the two. Applicants applied three difference levels of DCvoltage to the E-O cell in order to change the maximum availablepointing slope. The results showed a minimum speckle intensitynormalized standard deviation at about 57 ns relative timing. Withoutany angular shift during the seed pulse, at both small and largerelative timing values, below and above 57 ns the speckle contrast ishigh. This correlates with values found by applicants during statictesting. When, e.g., the relative timing places the E-O Cell voltageslope coincident with the seed pulse, the speckle pattern of a singlepulse is smeared in the vertical direction, in a dramatic andsatisfactory way.

Required limits on ASE as currently understood are believed to beattainable with around 5 uJ of seed laser energy and below, e.g., with along seed pulse shape. Saturation test results have shown applicantsthat output energy can be attained and the same ASE upper limit levelscan be achieved with only 3.75 uJ of seed laser energy when using ashort duration seed pulse. Further reductions in seed pulse durationmight be possible, resulting in even smaller seed energy requirements.However such further reductions in seed energy may be unnecessary sinceapplicants envision using ˜10 uJ of solid state 193 nm seed energy.Shorter pulse durations may prove difficult since, e.g., two stages ofmini-OPuS may be used, e.g., between seed laser and the poweramplification stage, with a requirement that the delay length of eachmini-OPuS be greater than the seed laser pulse duration, the resultingstretched pulse then being approximately 10 ns FWHM.

One can normalize contrast values to the maximum value in order toevaluate the percentage reduction in contrast, e.g., brought about bythe dynamic pointing shift. At the optimum relative timing point thespeckle contrast was found to be reduced to about 40% of its peak. Usingthe assumption for equivalent number of independent pulses the data canbe used to derive the number of pulses required to achieve this level ofspeckle contrast reduction. At the optimum relative timing, and with 3kV applied to the E-O cell, the contrast reduction was found to beequivalent to 6 pulses. Even higher voltage levels (and thus even largerpointing shift during a single pulse) could improve this result.Applicants performed similar measurements with the seed laser pulseentering the power amplification stage cavity, but no discharges betweenthe amplification stage electrodes and noted that reflections from theOC and the Rmax in the XeF cavity, from the OPuS effect, beam spreadingalone, indicated that the maximum speckle contrast was reduced by theamount predicted by the OPuS effect (N=1.56 with a 20% OC, giving1/√{square root over (n)}=0.80. Thus 70% contrast becomes 56%). Theeffect of smearing, even though the initial speckle contrast is lower,appears not to change when adding the secondary reflections from thefull XeF cavity. The equivalent pulse for speckle reduction is stillabout 6.

Applicants performed similar measurements with amplification stagecavity electrodes discharging and thus implicating the effects of theamplification within the amplification stage cavity, which indicated asshown in FIG. 17 the decrease in the impact on speckle reduction throughseed beam sweeping. With such a configuration, the effect was found tobe just over half of the equivalent number of pulses produced, i.e.,about 3, when operating as a MO/amplification stage, also found was arather large reduction in peak speckle contrast, with no smearing.Previous measurements of MO/amplification stage operation showed areduction equivalent to about 6 pulses. These results show a reductionequivalent to about 8 pulses. Applicants suspect that the amplificationstage cavity may discriminate against off-axis ray angles, e.g., in aflat-flat cavity, and thus the spray of angles sent into the cavity maynot all be equally amplified (this could be corrected, e.g., with a truestable cavity, e.g., employing a curved OC and a curved Rmax). Anotherexplanation may be that not all of the seed pulse takes part incontrolling the amplification stage characteristics. Maybe only, e.g.,the first 5 ns of the seed pulse's 10-15 ns pulse duration controls theamplification stage and thus the E-O sweep is not fast enough to occurwithin that smaller window. This may also be corrected, e.g., by using asmaller resister and a shorter sweep.

Turning to FIG. 47 there is illustrated schematically and in blockdiagram form a laser treatment system, e.g., and LTPS or tbSLS laserannealing system, e.g., for melting and recrystallizing amorphoussilicon on sheets of glass substrates at low temperature. The system1070 may include, e.g., a laser system 20 such as described herein and aoptical system 1272 to transform the laser 20 output light pulse beamfrom about 5×12 mm to 10 or so microns×390 mm or longer thin beams fortreating a workpiece, e.g., held on a work piece handling stage 1274.

It will be understood by those skilled in the art that disclosed hereinis a method and apparatus which may comprise a line narrowed pulsedexcimer or molecular fluorine gas discharge laser system which maycomprise a seed laser oscillator producing an output comprising a laseroutput light beam of pulses which may comprise a first gas dischargeexcimer or molecular fluorine laser chamber; a line narrowing modulewithin a first oscillator cavity; a laser amplification stage containingan amplifying gain medium in a second gas discharge excimer or molecularfluorine laser chamber receiving the output of the seed laser oscillatorand amplifying the output of the seed laser oscillator to form a lasersystem output comprising a laser output light beam of pulses, which maycomprise a ring power amplification stage. The ring power amplificationstage may comprise an injection mechanism which may comprise a partiallyreflecting optical element, e.g., a beam splitter through which the seedlaser oscillator output light beam is injected into the ring poweramplification stage. The ring power amplification stage may comprise abow-tie loop or a race track loop. The ring power amplification stagemay amplify the output of the seed laser oscillator cavity to a pulseenergy of ≧1 mJ, or ≧2 mJ, or ≧5 mJ, or 10 mJ, or ≧15 mJ. The lasersystem may operate at an output pulse repetition rate of up to 12 kHz,or ≧2 and ≦8 kHz, or ≧4 and ≦6 kHz. The apparatus and method maycomprise a broad band pulsed excimer or molecular fluorine gas dischargelaser system which may comprise a seed laser oscillator producing anoutput comprising a laser output light beam of pulses which may comprisea first gas discharge excimer or molecular fluorine laser chamber; alaser amplification stage containing an amplifying gain medium in asecond gas discharge excimer or molecular fluorine laser chamberreceiving the output of the seed laser oscillator and amplifying theoutput of the seed laser oscillator to form a laser system output whichmay comprise a laser output light beam of pulses, which may comprise aring power amplification stage. The ring power amplification stage maycomprise an injection mechanism comprising a partially reflectingoptical element through which the seed laser oscillator output lightbeam is injected into the ring power amplification stage. The ring poweramplification stage may comprise a bow-tie loop or a race track loop.The apparatus and method may comprise a coherence busting mechanismintermediate the seed laser oscillator and the amplifier gain medium.The coherence busting mechanism may comprise an optical delay pathhaving a delay length longer than the coherence length of a pulse in theseed laser oscillator laser output light beam of pulses. The opticaldelay path may not substantially increase the length of the pulse in theseed laser oscillator laser output light beam of pulses, but not createoverlapping pulses, e.g., as occurs in a 4×OPuS sold by applicants'assignee, with a delay path of many meters, which also significantlyincreases the T_(is) of the pulse as well as its temporal and spatiallength. The coherence busing mechanism may comprise a first opticaldelay path of a first length and a second optical delay path of a secondlength, with the optical delay in each of the first and second delaypaths exceeding the coherence length of a pulse in the seed laseroscillator laser output light beam of pulses, but not substantiallyincreasing the length of the pulse, and the difference in the length ofthe first delay path and the second delay path exceeding the coherencelength of the pulse. The apparatus and method may comprise a linenarrowed pulsed excimer or molecular fluorine gas discharge laser systemthat may comprise a seed laser oscillator producing an output comprisinga laser output light beam of pulses that may comprise a first gasdischarge excimer or molecular fluorine laser chamber; a line narrowingmodule within a first oscillator cavity; a laser amplification stagecontaining an amplifying gain medium in a second gas discharge excimeror molecular fluorine laser chamber receiving the output of the seedlaser oscillator and amplifying the output of the seed laser oscillatorto form a laser system output comprising a laser output light beam ofpulses, which may comprise a ring power amplification stage; a coherencebusting mechanism intermediate the seed laser oscillator and the ringpower amplification stage. The ring power amplification stage maycomprise an injection mechanism comprising a partially reflectingoptical element through which the seed laser oscillator output lightbeam is injected into the ring power amplification stage. The coherencebusting mechanism may comprise an optical delay path having a delaylength longer than the coherence length of a pulse in the seed laseroscillator laser output light beam of pulses. The optical delay path maynot substantially increase the length of the pulse in the seed laseroscillator laser output light beam of pulses. The coherence bustingmechanism may comprise a first optical delay path of a first length anda second optical delay path of a second length, with the optical delayin each of the first and second delay paths exceeding the coherencelength of a pulse in the seed laser oscillator laser output light beamof pulses, but not substantially increasing the length of the pulse, andthe difference in the length of the first delay path and the seconddelay path exceeding the coherence length of the pulse. The coherencebusting mechanism may comprise a coherence busting optical delaystructure generating multiple sub-pulses delayed sequentially from asingle input pulse, wherein each sub-pulse is delayed from the followingsub-pulse by more than the coherence length of the pulse light. Theapparatus and method may comprise a broad band pulsed excimer ormolecular fluorine gas discharge laser system which may comprise a seedlaser oscillator producing an output comprising a laser output lightbeam of pulses which may comprise a first gas discharge excimer ormolecular fluorine laser chamber; a laser amplification stage containingan amplifying gain medium in a second gas discharge excimer or molecularfluorine laser chamber receiving the output of the seed laser oscillatorand amplifying the output of the seed laser oscillator to form a lasersystem output comprising a laser output light beam of pulses, which maycomprise a ring power amplification stage; a coherence busting mechanismintermediate the seed laser oscillator and the ring power amplificationstage. The ring power amplification stage may comprise an injectionmechanism comprising a partially reflecting optical element throughwhich the seed laser oscillator output light beam is injected into thering power amplification stage. The coherence busting mechanism maycomprise an optical delay path having a delay length longer than thecoherence length of a pulse in the seed laser oscillator laser outputlight beam of pulses. The optical delay path may not substantiallyincrease the length of the pulse in the seed laser oscillator laseroutput light beam of pulses. The coherence busing mechanism may comprisea first optical delay path of a first length and a second optical delaypath of a second length, with the optical delay in each of the first andsecond delay paths exceeding the coherence length of a pulse in the seedlaser oscillator laser output light beam of pulses, but notsubstantially increasing the length of the pulse, and the difference inthe length of the first delay path and the second delay path exceedingthe coherence length of the pulse. The coherence busting mechanismcomprising a coherence busting optical delay structure generatingmultiple sub-pulses delayed sequentially from a single input pulse,wherein each sub-pulse is delayed from the following sub-pulse by morethan the coherence length of the pulse light. The apparatus and methodmay comprise a pulsed excimer or molecular fluorine gas discharge lasersystem which may comprise a seed laser oscillator producing an outputcomprising a laser output light beam of pulses which may comprise afirst gas discharge excimer or molecular fluorine laser chamber; a linenarrowing module within a first oscillator cavity; a laser amplificationstage containing an amplifying gain medium in a second gas dischargeexcimer or molecular fluorine laser chamber receiving the output of theseed laser oscillator and amplifying the output of the seed laseroscillator to form a laser system output comprising a laser output lightbeam of pulses; a coherence busting mechanism intermediate the seedlaser oscillator and the laser amplification stage comprising an opticaldelay path exceeding the coherence length of the seed laser output lightbeam pulses. The amplification stage may comprise a laser oscillationcavity. The amplification stage may comprise an optical path defining afixed number of passes through the amplifying gain medium. The coherencebusting mechanism may comprise an optical delay path having a delaylength longer than the coherence length of a pulse in the seed laseroscillator laser output light beam of pulses. The optical delay path maynot substantially increase the length of the pulse in the seed laseroscillator laser output light beam of pulses. The coherence bustingmechanism may comprise a first optical delay path of a first length anda second optical delay path of a second length, with the optical delayin each of the first and second delay paths exceeding the coherencelength of a pulse in the seed laser oscillator laser output light beamof pulses, but not substantially increasing the length of the pulse, andthe difference in the length of the first delay path and the seconddelay path exceeding the coherence length of the pulse.

Applicants have simulated through calculations speckle reduction asrelates to the location of coherence lengths within a single gasdischarge (e.g., ArF or KrF excimer) laser system output pulse aftersuch a pulse has passed through the two OPuS pulse stretchers sold onlaser systems manufactured by applicants' assignee Cymer, Inc., used forpulse stretching to increase the total integrated spectrum (T_(is)) toreduce the impact of peak intensity in the laser output pulse on theoptics in the tool using the output light from the laser system, e.g., alithography tool scanner illuminator. There are two OPuS in series, withthe first having a delay path sufficient to stretch the T_(is) of theoutput pulse from about 18.6 ns to about 47.8 ns and the second tostretch the pulse further to about 83.5 ns.

Starting with the unstretched pulse, applicants divided the pulse intoportions equal to the approximate coherence length, assuming a FWHMbandwidth of 0.10 pm and a Gaussian shape for the coherence lengthfunction. The impact of the pulse stretching on the coherence lengthportions of the pulse after passing through the first OPuS was to showthat a first intensity hump in the stretched pulse was made up of thecoherence length portions of the main pulse, a second intensity hump wasmade up of coherence length portions of the main pulse overlapped withcoherence length portions of a first daughter pulse. A third hump in theintensity of the stretched pulse is the result of overlapping of thefirst and second daughter pulses. Looking at the individual coherencelength portions of the two humps applicants observed that the multipleversions (including daughters) of the coherence length portions remainedsufficiently separated to not interfere with each other.

After passage through the second OPuS the simulated intensity of thestretched pulses, again only looking at the content of the first threehumps in the stretched pulse, in the simulation (under the second humpwere contributions from the original undelayed pulse, as before, thefirst delayed pulse from the first OPuS, as before, and the firstdelayed pulse from the second OPuS), applicants observed that in thissecond pulse the multiple versions of the coherence length portions werevery close together. This is caused by the fact that the first OPuS hasa delay of ˜18 ns and the second has a delay of ˜22 ns. Thus only ˜4 nsseparates the versions of the coherence length portions, which is stillnot close enough for interference.

Under the third hump applicants observed contributions from the firstdelayed pulse from the first OPuS, the second delayed pulse from firstOPuS, the first delayed pulse from the second OPuS, and the seconddelayed pulse from second OPuS. Applicants observed that the separationbetween some related coherence portions is larger than for others in thethird hump in the intensity plot of the pulse stretched by two OPuSs.This increase in separation is due to the fact that two round tripsthrough each OPuS equal ˜36 ns=18*2 and ˜44 ns=22*2. Thus the separationbetween coherence lengths grows with each round trip.

Applicants concluded that for a mini-OPuS as described in thisapplication a single mini-OPuS with delay equal to one coherence lengthwill create a train of pulses that dies out after about 4 coherencelength values. Thus, applicants determined that for a single mini-OPuSto be effective, the two main OPuSs should not bring any daughtercoherence lengths to within 4 coherence lengths of each other. But,applicants have observed in the simulation that the main OPuSs do justthat, though only marginally so. The separation between coherencelengths for the third and greater humps is sufficient. Applicantsbelieve that the impact of a single mini-OPuS between MO andamplification gain medium will be nearly the full expected coherencebusting effect. A second mini-OPuS between MO and PA may not adequatelyinteract with the two main OPuSs. The empty spaces, not filled withrelated coherence length portions of the pulse humps get more scarcewhen one combines a single min-OPuS and two regular OPuSs, and thesecond may be too much. According to aspects of an embodiment of thepresent invention applicants propose the coordinated change of theregular OPuS delay lengths when the mini-OPuS(s) are installed,including whether they are part of the laser system or installed downstream of the regular main OPuSs, e.g., in the lithography tool itself.Applicants believe that such mini-OPuS(s) can fill in the valleys of thepulse duration somewhat, leading to an increase in T_(is), e.g.,allowing a reduction in the delay lengths of one of the two main OPuSsfor better overall coherence length separation.

According to aspects of an embodiment of the disclosed subject matterthere are certain performance requirements necessary of a very highpower amplification stage cavity for, e.g., a 120-180 W or higher lasersystem, e.g., with two amplifier gain medium chambers in parallel. Theyshould produce linear polarization (>98%). Each amplification stageshould produce, and survive, ≧60 W average output energy, e.g., at 193nm wavelength of ArF, or less stringently at longer wavelengths, e.g.,248 for KrF and 351 for XeF or 318 for XeCl, though even more stringentfor F₂ at 157 nm. Each amplification stage in one embodiment may operateat about 6 kHz or above. According to aspects of an embodiment of thedisclosed subject matter, the amplification stage(s) can exhibit fullseeding (at or near saturation) with relatively small seed laser energy.According to aspects of an embodiment of the disclosed subject matterseed laser energy may be no more than around 1 μJ, though the systemoverall output power in such cases may be less than 200 W. Applicantsbelieve that the amplification stage should also support a moderatelylarge angular distribution, e.g., to maintain the same angular spread ofthe seed laser, in order to avoid inadvertently improving coherence by,e.g., removing coherence cells, e.g., with a range of angles of within afew m Rad. Protection of the seed laser from reverse traveling radiationis also an important operational requirement. When properly seeded, ASElevels produced by the amplification stage, according to aspects of anembodiment of the disclosed subject matter, should be less than 0.1% orless of the total output.

According to aspects of an embodiment of the disclosed subject matterapplicants expect that (1) the gain cross-section will be similar toexisting ArF chambers, e.g., applicants' assignee's XLA ArF laser systempower amplifier (“PA”) chambers, (2) the gain length will also besimilar to existing ArF chambers, (3) the gain duration will also besimilar to existing ArF chambers.

According to aspects of an embodiment of the disclosed subject matter,applicants propose, e.g., a single MO/gain amplification medium XLAtic-toc with a solid state seed laser operating at 12 kHz with about a 1mJ seed laser output light pulse energy and the two amplification stageseach operating at around a 17 mJ output pulse energy. In addition,according to aspects of an embodiment of the disclosed subject matter,applicants propose the utilization of a regenerative gain media, e.g., aring power amplification stage, which can enable the generation ofseveral times the output pulse energy in the ring power amplificationstage compared, e.g., to a power amplifier (“PA”) in a MOPAconfiguration. For testing purposes applicants have simulated the inputfrom a solid state 193 nm seed laser using a line-narrowed ArF laser.

Applicants have studied ASE vs. MO-PO timing difference for thedifferent values of the above noted parameters with results as indicatedin FIG. 7. Similarly a study of MOPO energy vs. MO-PO timing as afunction of these same parameters also illustrated in FIG. 7.

In order to meet the requirements noted above, including, e.g., theconstraints of known lithography laser light source technology,applicants propose, according to aspects of an embodiment of thedisclosed subject matter, a number of overall architectures that arebelieved to provide workable ways to address the requirements andconstraints noted above. The first may be to provide two multi-chamberlaser systems along the lines of applicants' assignee's XLA XXX lasersystem series, e.g., with two dual chamber laser oscillator/amplifierarrangements whereby each is configured to run at around 6 kHz producingoutput pulses at about 17 mJ with interleaved firing times to produce asingle approximately 12 kHz system producing about 17 m per pulse.

Thus, e.g., according to aspects of an embodiment of the disclosedsubject matter, illustrated schematically and in block diagram form inFIG. 54, a very high average power laser system, e.g., an immersionlithography laser light source 1520 may comprise a plurality ofoscillator/amplifier laser system output light pulse beam sources, e.g.,1522, 1524, each of which comprising, e.g., a master oscillator portioncomprising master oscillator chambers 1530, such as those being sold byapplicants' assignee Cymer Inc. as part of an existing XLA XXX modelmulti-chamber laser system. Also included in each oscillator/amplifierlaser system 1522, 1524 may be a power amplifier portion 1532, e.g.,comprising an amplifier gain medium. Each of the twooscillator/amplifier laser systems 1522, 1524 provide an output lightpulse beam to a beam combiner 1540, e.g., in an overleaving fashion.

Thus, e.g., with each laser system 1522, 1524 operating at 6 kHz and 17mJ output laser light pulse beam pulse energy the combined output fromthe beam combiner 1540 could be a 12 kHz 17 mJ output resulting in abouta 200 W average power laser system. It will also be understood that theembodiment of FIG. 54 may also be implemented with, e.g., a furtherplurality of identical oscillator amplifier laser systems 1526, 1528 toproduce a 400 W average power laser system. Alternatively, each of theoscillator/amplifier systems 1522, 1524, 1526, 1528 could, e.g., operateat less than 6 kHz, e.g., each at 4 kHz and/or with a higher overalloscillator/amplifier system 1522, 1524, 1526, 1528 output laser lightpulse beam pulse energy, e.g., up to around 33 mJ, to the extent thatoptical damage limits and cost of operation and other factors willallow, for various combinations of ultimate output 100 pulse repetitionrate and pulse energy for a similar variety of average output powervalues from the system 1520.

Referring now to FIG. 55 there is illustrated schematically and in blockdiagram form a very high average power tic-toc seed laser/amplifiersystem 1550 according to aspects of an embodiment of the disclosedsubject matter. The seed laser amplifier system 1550 may include, e.g.,a seed laser portion 1530, e.g., a solid state seed laser such as aNd:YAG or a Nd:YLF or a Ti:Sapphire or a fiber laser or other solidstate laser, or an excimer or molecular fluorine gas discharge seedlaser, e.g., operating at around 12 kHz with a 1-2 mJ output energypulse and a pair of amplifier portions 1532, each being supplied with,e.g., the alternating output pulses from the seed laser portion 1530,e.g., through a beam splitter 1552, discussed in more detail elsewherein the present application. The pulse could be supplied in other than analternating fashion, depending on the repetition rates of theamplification stages. Each of the amplifier portions 1532 can then berun at, e.g., around 6 kHz for a 200 W output with only a 17 mJ outputfrom each of the amplifier portions 1532. Moreover, seed lasers, couldbe selected to operate at in a range of about 4-12 kHz, giving anoutput, e.g., for a two amplification stage in parallel embodiment, of 8kHz to 24 kHz.

Referring to FIG. 56 there is shown schematically in block diagram forman example of a very high average power multiple tic-toc seedlaser/amplifier system 1570 according to aspects of an embodiment of thedisclosed subject matter. The system 1570 may include, e.g., a first anda second seed laser 1572 each supplying seed laser pulses to a pair ofamplifier portions, e.g., amplifier gain media 1574, through a beamsplitter 1552 and with the output of each combined in a beam combiner1578 to provide a laser light source system output laser light pulsebeam 100 with an average output power of at or above 200 W. The seedlasers could be, e.g., solid state lasers operating at, e.g., around 12kHz and the amplifier portions could be, e.g., gas discharge lasers,e.g., excimer or molecular fluorine lasers operating at around 6 kHz.Alternatively, e.g., the seed lasers 1572 could be excimer lasers, e.g,KrF, ArF, XeCl, XeF or molecular fluorine lasers operating at about 6kHz with the respective pairs of tic-toc amplifier portions eachoperating at 3 kHz for a total of 12 kHz and 17 mJ per lithography orLTPS laser light source system output laser light pulses and a resultantaverage power of around 200 W. Frequency conversion, as discussed inmore detail elsewhere in the present application may be needed to shiftthe wavelength of the seed laser(s) 72, e.g., solid state lasers, up tothe wavelength of the gas discharge laser amplifier portions 1574. Thebeam combiner 1578 may be a single beam combiner as shown or cascadingcombiners as shown in the combiners 1540, 1542 in FIG. 54.

It will also be understood by those skilled in the art that variouscombinations and permutations of the arrangement illustrated in FIG. 56may be utilized. For example there may be a plurality of A seed lasers1572 operating at X kHz with each seeding a plurality of B amplifierportions 1574, each operating at X/B kHz and the combination providingAX system output laser light source output pulses in the output beam 100of FIG. 56. Then, depending on the necessary average system outputpower, the pulse energy for the output of each of the plurality ofamplifier portions 74 may be determined, e.g., with A=2 and B=2, asillustrated in FIG. 56 and X=6 kHz the overall output beam 100 can havea 12 kHz output and with 17 mJ pulses out of the amplifier portions onegets around 200 w of average output power. The same may be said for thepossible arrangements of FIG. 54.

It will be noted that a tic-toc amplifier LTPS or immersion lithographylight source, e.g., seeded by a master oscillator running at, e.g.,twice the repetition frequency of the, e.g., two amplifier chambers,could be two excimer laser chambers in a MO/amplification gain mediumconfiguration. For example, each amplification medium could have arecirculating/regenerative ring power amplification stage, each of whichis alternatively seeded by a master oscillator running at twice therepetition rate of either amplification stage excimer laser chamber.Such systems can be run at any of the desired wavelengths, e.g., DUVwavelengths, e.g., with the MO and PA/PO operating at 157 nm (F₂), 193nm (ArF), 248 nm (KrF), 308 nm (XeCl) or 351 nm (XeF). Further, suchsystems could include solid state or excimer seed lasers operating at ahigher pulse repetition rate seeding a plurality of power amplificationstages, e.g., two, in tic-toc configuration, such as ring poweramplification stages.

In FIG. 57 there is shown partly schematically and partly in blockdiagram form, by way of example an immersion laser lithography system1580 according to aspects of an embodiment of the disclosed subjectmatter. The system 1580 may include, e.g., a very high average poweroutput laser light pulse beam source 1520 such as shown in FIG. 54 or1550 such as shown in FIG. 55 or 1570 such as shown in FIG. 56,supplying line narrowed pulses at 200 W or above average power to ascanner 1590, such as those made by ASML or Canon or Nicon. The scanner1590 may incorporate an illuminator 1592, a reticle 1594 and a waferstage 1596 carrying a wafer 1598 for exposure by the radiation from thelight source 1520. On the wafer stage 1596 may be a liquid source 1602,e.g., with the liquid being water having a different index of refractionthan the ambient around the reticle 1594 and stage 1596, and a liquiddrain 1604, supplying the liquid 1606 to cover the wafer 1598 forimmersion lithography.

It will also be understood that for purposes of coherence busting,either for excimer or other gas discharge seed lasers supplying excimeror other gas discharge laser amplifier portions or for solid state seedlasers, use of multiple amplifier portions with the beams combined asnoted elsewhere in the present application may have beneficial effectsin decreasing the optical coherency and therefore, assisting in reducingthe effects of the speckle, e.g., in integrated circuit photolithographyor LTPS or tbSLS processing. It will also be understood that one or moreof the various coherence busting techniques and/or combinations thereofdisclosed herein may be utilized inside of the scanner 1590, whetherthat scanner 1590 is an immersion scanner or not.

Turning now to FIG. 58 there is shown schematically and in block diagramform a solid state seed laser to gas discharge amplifier laser system1620 according to aspects of an embodiment of the disclosed subjectmatter. The system 1620 may include, e.g., a solid state pulsed seedlaser 1622, e.g., an Nd:YAG or an ND:YLF pumped tunable solid statelaser 1622. The output of the laser 1622 may pass through a coherencebuster/frequency multiplier 1626, which may, e.g., be a single opticalelement, e.g., capable of both frequency shifting the output of the seedlaser 1622 and beam steering, as is explained in more detail elsewherein this application with respect to coherency busting, or could be afrequency shifter along with a coherency buster in series, e.g., asshown in FIG. 59 The system may also have, e.g., an amplifier gainmedium such as a PA or PO 1624, or, e.g., a ring power amplificationstage 1624, e.g., with the output 100 supplied to a scanner 1590 (Shownin FIG. 57).

It will be understood that with various tuning mechanisms may be used,e.g., operating temperature, as is know in the art, the solid statelaser, e.g., a 1064 nm wavelength Nd:YAG (neodymium-doped yttriumaluminum garnet (Nd:Y₃Al₅O₁₂)), or 1053 nm Nd:YLF (neodymium dopedyttrium lithium fluoride) or Ti:Sapphire laser (tunable from about 650to 1100 nm), and/or by line selection. The desired frequency/wavelengthfor amplification in the amplifier portion 1624 may be attained, e.g.,with the frequency up-converter 1626 to within an acceptable Δλ from thenominal center wavelengths of around 351 for XeF, 248 for KrF, 193 forArF and 157 for molecular fluorine to have acceptable amplifying lasingoccur in the amplifier portion 1624, as is well understood in the art.As noted above, coherency busting of the type discussed elsewhere hereinmay be used inside the scanner 1590 or other application tool, e.g.,another micro-lithography tool or a thin beam laser annealing tool.

Turning to FIG. 59 there is shown in block diagram form a solid stateseed laser/amplifier laser system 1620 according to aspects of anembodiment of the disclosed subject matter similar to that of FIG. 69wherein, e.g., a frequency multiplier 1630 and a coherence buster 1632may be utilized to provide appropriate seed pulses to the amplifierlaser portion 1624 to accommodate, e.g., the high coherency of the seedlaser output laser light pulse beam pulses and also their frequencyshift to the desired frequency/wavelength for amplification, e.g., inthe gas discharge amplification gain medium of the amplification stage1624. The frequency multiplier 1630 and coherence buster 1632, as is thecase in other arrangements noted herein, may be combined, e.g., a singlenon-linear crystal may be used for both, e.g., with appropriate drivesignals as will be understood by those skilled in the art, or multiplecrystals may be used, e.g., with some crystals optimized for frequencyconversion and the others for coherency busting, and positions may beswapped, i.e., coherence busting followed by frequency shifting andvice-versa.

Turning to FIG. 60 there is shown schematically and in block diagramform conversion of the output of a seed laser, e.g., with a frequencyconverter 1630 along with a beam divider 1640, followed by coherencybusting in one axis, e.g., the long axis of the laser beam or a firstaxis if the beam is not an ellipse or an elongated rectangle and theshort axis or a second orthogonal axis if the beam is not an elongatedrectangle, with a respective vertical axis coherency buster 1642 andhorizontal axis coherency buster 1644, as explained in more detailherein. The outputs of the coherency busters 1642, 1644 may be combinedin a beam combiner 1646, which, as noted elsewhere, may also serve acoherency busting role, e.g., as shown in connection with FIG. 31,and/or FIGS. 37 A and B, and provided as seed laser pulses to theamplifier gain medium portion 1648. Otherwise, if suitable non-linearcrystals may not be found for such an embodiment, coherence busing maybe don in one axis, e.g., in a coherency buster 1642, followed in seriesby coherency busing in a second axis in a coherency buster 144, withoutthe need for the subsequent beam combiner 1646.

Turning to FIG. 61 there is shown schematically and in block diagramform a version of the embodiment of FIG. 60 in which, e.g., thefrequency conversion in a frequency converter 1630 occurs after thecoherency busting, i.e., intermediate the beam combiner 1646 and theamplifier portion 1648.

According to aspects of an embodiment of the disclosed subject matterthe generation of 351 nm radiation, e.g., coherent 351 nm radiation, canbe done with a solid-state configuration having, e.g., a solid-statedrive laser (or lasers) that drive linear or nonlinear frequencyconversion stages. Generation of 351 nm laser radiation can be, asillustrated, attained by third harmonic conversion of the output of aNd:YLF laser operating at 1053 nm. In order to use this approach as aseed laser for an XeF excimer amplifier/oscillator, however, one mustensure that the nominal center wavelength of the, e.g., Nd:YLF seedlaser master oscillator matches the gain spectrum of XeF (two lines at351.12 and 351.26 nm). An alternative approach could be to use anYb-doped fiber laser as the fundamental drive laser seed pulse source.Yb3+ fiber lasers are inherently tunable, as discussed in J Nilsson etal “High-power wavelength-tunable cladding-pumped rare-earth-dopedsilica fiber lasers,” Opt. Fiber Technol. 10, pp 5-30 (2004), to allowoperation between 1050 and 1065 nm. Fiber lasers offer somesimplifications in design that may be of particular benefit inapplications requiring ultra-reliability, such as LTPS andmicrolithography. Applicants propose using a pulsed fiber laser systemas the source of moderate peak power (5-50 kW) high-repetition-rate(multi-kHz, e.g., up to about 12-15 kHz) 1054 nm narrowband pulsedradiation. Such a laser could be constructed using standard Yb³⁺ pulsedfiber laser technology—either a q-switched fiber oscillator, a pulseddiode source that is fiber amplified, or a CW source (fiber oscillatoror diode) that is modulated (internally or externally) and is fiberamplified.

After the 1054 nm radiation is generated, it can, e.g., be frequencyupconverted directly to, e.g., about 351.2 nm, using two stages ofnonlinear frequency conversion (second harmonic generation (“SHG”) of1054 to 527 nm then sum frequency generation (“SFG”) with the residualfundamental to 351.2 nm (with ˜+/−0.1 nm bandwidth).

A CW solid state laser, e.g., a diode laser, with a very narrowbandwidth (very high spectral purity), e.g., matched to the fiber laser,to provide a very narrow band seed to the pulsed solid state fiber laserfor amplification and the production of a very narrow band pulsed solidstate seed to the power amplification stage(s), e.g., for KrF or ArFlasers. Appropriate LMA (large-mode area) fiber technology may be usedto minimize spectral degradation due to nonlinear effects in the fibercomprising the fiber laser amplification oscillator or any subsequentamplification stages. Using such approaches allows spatial beam qualityto be maintained (there are techniques for ensuring single-modeoperation in large mode area fibers) while reducing the peak power inthe core of the fiber.

A fiber-laser-based solid-state 351 nm MO, for XeF, can also be realizedaccording to aspects of an embodiment of the disclosed subject matter.Such a master oscillator architecture may be a simpler more robustsolution than a bulk-solid-state laser.

Turning now to FIGS. 62-65 there are shown schematically and partly inblock diagram form a plurality of injection seeded 351 nm gas dischargemaster oscillator/amplifier gain medium laser system solid state masteroscillators 1700 according to aspects of an embodiment of the disclosedsubject matter. The master oscillator 1700 may include, e.g., a Yb³⁺doped fiber oscillator or amplifier 1710, e.g., with a diode pump 1712and a seed laser, e.g., a 1054 nm CW seed diode laser 1714.

Referring to FIG. 62 the master oscillator oscillation cavity may beformed by a rear cavity fully reflective mirror 1720 and a partiallyreflective output coupler 1722, which may be 90% reflective at thenominal 1054 nm center wavelength of the fiber oscillator 1710. Themaster oscillator 1700 may employ a Q switch 1724 to allow for theoutput pulse energy of the master oscillator 210 to accumulate in theoscillation cavity until sufficiently high in energy before the Q-switch1724 is opened, as is well known in the art. The output of the masteroscillator 1700 may thus be pulsed by the frequency of operation of theQ-switch, e.g., at a rate of about 12 kHz. The output of the fiberoscillator laser 1710 may be passed through a second harmonic generator1730, followed by a frequency adder 1732, to add the original frequencyto the second harmonic to generate a third harmonic, i.e., a wavelengthof about 351 nm suitable for amplification, in, e.g., a XeF gasdischarge laser power amplifier or power oscillator or ring poweramplification stage amplifying gain medium (not shown in FIGS. 62-65).

Turning to FIG. 63 there is shown schematically and partly in blockdiagram form a solid state master oscillator 1700 according to aspectsof an embodiment of the disclosed subject matter. In this embodiment anexternal amplitude modulator 1740, e.g., an acousto-optic orelectro-optic switch or other suitable mechanism, may be used to pulsethe CW seed 1714 into the fiber amplifier 1710 to produce a pulsedoutput of the master oscillator 1700.

In the embodiment of FIG. 64 the 1054 seed may utilize, e.g., a pulsedseed diode 1750 to produce a pulsed output out of the master oscillator1710, e.g., at around 12 kHz. In the embodiment of FIG. 65 a tunable CWYb³⁺ master oscillator 1760 may be switched into the fiber amplifier1710 with an external amplitude modulator, such as is discussed above,to get a pulsed seed laser output from the master oscillator 1700. Thefiber amplifier 1710 may utilize pump diodes 1712 to pump the fiberamplifier 1710. The fiber laser may comprise a single fiber or amultiplicity of fibers, e.g., placed serially, with each fiberoptimized, as is known in the art, for amplification of its inputsignal.

According to aspects of an embodiment of the disclosed subject matterapplicants have determined certain characteristics desirably evidencedby a seed laser, e.g., a solid state seed laser, for a very high averagepower laser system, e.g., for photolithography or LTPS applications,including, e.g., pulse energy, pulse duration and timing jitter, whichcan drive the selection of a seed laser, e.g., a solid state seed laserto the choice(s) of Nd:YAG, Nd:YLF, Ti:Sapphire, and fiber lasers, asdiscussed elsewhere.

According to aspects of an embodiment of the disclosed subject matterapplicants have also studied certain amplification stage resonatorcavity properties. On the one hand may be a flat-flat cavity with simplebeam splitter input/output coupling, which is simple of construction,though perhaps more wasteful of seed laser energy than is practical in aproduction system. On the other hand may be a recirculating orregenerative power oscillator, e.g., a ring power amplification stage,e.g., with a beam splitter/mirror input/output coupler. It will beunderstood by those skilled in the art, as noted above, terms likeoscillator, cavity and the like used in reference to, e.g., a MOPOconfigured laser system mean that the amplification portions of thelaser system, seeded by a seed laser portion, lasers due to stimulatedemission from the seed beam pulse oscillating in the cavity. This isdistinguished from what may be referred to as a power amplifier, such asthe PA portions of applicants' assignee's MOPA configured XLA XXX serieslaser systems. By contrast the amplification occurs in a power amplifierby stimulated emission during a gas discharge in the amplification gainmedium of the amplifier portion of the laser system as the seed laserpulse is directed through the amplification gain medium in an excitedstate a fixed number of times by an optical arrangement, e.g., a twopass optical system as used in applicants' assignee's current XLA XXXseries laser systems. In some of the literature, however, an amplifierwith a closed cavity around the amplification gain medium, e.g., abow-tie or racetrack loop path length may be considered to be a “poweramplifier” or a regenerative amplifier rather than a “power oscillator.”Therefore for purposes of this application and the appended claims theuse of the term “ring power amplification stage” is intended to coverany of these structures where a power boosting stage incorporates a gainmedium with a closed optical cavity.

The flat-flat configuration may use a traditional polarizationinput/output coupling e.g., with a polarizing beam splitter and aquarter wave plate and partially reflective output coupler, e.g., asdescribed in more detail below with respect to FIGS. 66 and 69. This maymake more efficient use of the seed laser energy but could also be moresusceptible to, e.g., thermal effects at high pulse energy and/or highaverage output power. Other input/output coupling could also be employedas explained elsewhere in this application.

Turning now to FIGS. 14 and 16 there are illustrated in schematic andpartly block diagram form examples of very high power, e.g., around 200W or better average output power, laser systems, 280, and 450,respectively, according to aspects of an embodiment of the disclosedsubject matter. These laser systems 280, 450 may be used, e.g., forimmersion lithography use or for LTPS use, or the like, which mayinclude, e.g., in the case of FIG. 14 a ring power amplification stageconfigured laser system 280. The system 280 may include a seed laser286, which may provide seed laser pulses at, e.g., around 1.0 mJ or lessand a pulse repetition rate of, e.g., around 6 kHz, in a seed laseroutput light pulse beam 288 of laser output light pulses. The beam 288from the seed laser 286 may pass through a seed injection couplingmechanism 300 into an amplifier gain medium portion 290 of the lasersystem 280.

The amplifier gain portion 290 may comprise a ring power amplificationstage chamber 292 containing a pair of gas discharge electrodes 294 oneof which is seen in the view of FIG. 14. The chamber 292 may alsocomprise an input chamber section 296 and a beam reverser chambersection 298, each of which may be formed with or attached to, e.g., bysuitable leak proof means, the chamber 292, such that, e.g., the opticsin the input section 296 and in the beam reverser section 298 can bebeneficially exposed to fluorine in the lasing gas mixture enclosed inthe chamber sections 292, 296, 298.

The seed injection mechanism may include, e.g., a beamsplitter/input-output coupler 302 which may be coated with a coating orotherwise selected or made to be partially reflective to the seed laserlight, e.g., at a nominal center wavelength of around 193 nm for ArF,248 nm for KrF, 318 for XeCl or 351 for XeF laser systems, and amaximally reflective mirror 304 that is maximally reflective at theselected nominal center wavelength for the respective ArF, KrF, XeCl orXeF or the like gas discharge laser systems. The beam reverser 310 maybe similar to the power amplifier beam reversers, e.g., sold inapplicants' assignee's XLA MOPA configured laser systems, XLA XXXsystems. Such a beam reverser in an XLA-XXX may constitute a modulewhich may be part of a relay optics subsystem, that, e.g., directs thebeam from the output of the MO, through the PA, to the entrance of apulse stretcher to thereafter exit the laser system through the shutter.The relay optics subsystem may include an MO wavefrontengineering/steering box (“WEB”), a PA WEB and the beam reverser module.The Beam Reverser module receive the beam exiting the back end of the PAchamber and send it back through the PA chamber to the PA WEB at aspecified angle and position. The module contains the beam reverserprism, which steers the beam back through the PA chamber ensuring thatthe beam skims past a PA WEB turning prism which steered the beam intothe PA chamber in the first instance. The prism is adjustable along thex-axis and rotatable (tiltable) about the x-axis. The beam is returnedto the PA chamber on a slightly different path than from the PA WEB tothe beam reverser, e.g., as shown in FIG. 20-22, thereby, e.g., passingthrough the amplifier gain medium in the same path in the vertical axisand different crossing paths in the horizontal axis, horizontal andvertical being in relation to the electrodes and discharge lasingamplification medium and not necessarily oriented to and/orcorresponding to true horizontal and vertical. This forms the opticallydetermined tilted double pass of the seed beam from the seed laserthrough the power amplifier gain medium (not a sealed cavity) of a MOPApower amplifier such as noted above. The beam reverser may, e.g.,introduce a slight angle (a few milliradians) and a slight offset (a fewmillimeters) to the beam that is reflected back through the PA chamber,such that the two beams overlap inside the PA chamber (e.g.,intersecting at about the middle of the chamber length—middle of thelongitudinal length of the electrodes) and are spatially separated atthe PA WEB turning prism. The beam returner according to aspects of anembodiment of the subject matter disclosed may utilize a reverser prismwith no optical coatings. The beam may, e.g., enter and exit the beamreturner prism at near Brewster's angle, and total internal reflectionmay occur at the internal reflecting surfaces, thus there are, e.g.,virtually no surface losses. The prism must be made out of expensiveexcimer grade CaF₂. Birefringence, bulk absorption and scattering lossesmust be taken into account, but these phenomena are not expected to beproblematic.

In the input section 296 optically accessible through an input window312 may be placed a beam expander 320, which may be comprised of a prism322 and a prism 324, which together may narrow the beam 288 on its wayinto the chamber 292 and conversely expand it on its way out of thechamber 292, the expansion on the way out serving to, e.g., protect theoptical elements, e.g., the input/output coupler 300 and the narrowingof the beam 288 on the way into the chamber 292 serving to, e.g., narrowthe beam 340 entering the amplification gain medium to approximately thewidth of the discharge between the electrodes 294 in a directiongenerally perpendicular to the separation of the electrodes 294.

Baffles 330 may serve to, e.g., protect the optics in the input section296 and the beam reverser section 298 of the chamber 292 from damageresulting from, e.g., debris circulating with the lasing gas mixture inthe chamber 292.

Inside the cavity of the ring power amplification stage 290 the beam 288may take a first direction recirculating oscillation path 340 and returnon a second direction recirculating oscillation path 342 to the seedinjection mechanism 300 where the partially reflective input/outputcoupler acts as a traditional output coupler for an oscillator lasercavity and reflects part of the oscillating laser light photons to theRmax mirror 304 and back along the path 340. Thus the oscillation in thecavity formed by the seed injection mechanism 300 and the beam reverser310 is a multi-pass oscillation path. Such oscillation, as noted, isdistinct from the photons in a power amplifier making a fixed number ofpasses through the gain medium, e.g., two in applicants' assignee's XLAXXX laser systems, without oscillating along such power amplifier lightpath. When the oscillation in the recirculating/regenerative path 340,342 builds up enough pulse energy a laser system output laser lightpulse beam 100 is produced from the seeded power oscillator laser system280. The seed laser 286 could be either a gas discharge, e.g., excimeror fluorine laser or a solid state laser.

FIG. 16 illustrates schematically and partly in block diagram form aring power amplification stage laser system 490 configured similarly toapplicants' assignee's XLA XXX multi-chambered MOPA laser systems withthe PA replaced by a ring power amplification stage 490 according toaspects of an embodiment of the disclosed subject matter. The lasersystem 450 may be comprised of an excimer gas discharge laser seed laser452 which may comprise a master oscillator laser chamber 454, with aline narrowing module 456 having a reflective element, e.g., awavelength and bandwidth selective grating, forming a rear cavity mirrorand a partially reflective output coupler 458 forming the other end ofthe master oscillator 452 oscillation cavity. The master oscillator 452seed laser output laser light pulse beam of pulses leaving the outputcoupler 458 may pass through a metrology module (line center analysismodule “LAM”) 470, which may sample a portion of the output of the MOchamber 454, using a beam splitter 472, and also, in addition to awavemeter (not shown) for measuring nominal center wavelength of themaster oscillator seed laser output laser light pulse beam pulses maycomprise an MO laser output light pulse beam pulse energy monitor 474and an ASE monitor 476, such as a fluorescence detector. The ASEdetector, e.g., a broad band photodetector, may serve to detect thepresence of a high enough intensity of broadband light to indicate thetiming of the discharge in the amplification gain medium is off suchthat significant lasing in band is not occurring (the seed pulse is nottimed to be in the cavity of the amplification stage during thedischarge) and essentially only broad band lasing is occurring duringthe discharge in the amplification stage.

The master oscillator seed laser 452 output laser light pulse beam maythen pass to a turning mirror 480 and from there to a seed injectionmechanism 300 input to an amplifier gain medium portion 490, which maycomprise a ring power amplification stage chamber 492, having a chamberinput section 494 and a chamber beam reverser section 496. It will beunderstood by those skilled in the art that this schematic view of thelaser system 450 does not reflect various aspects of the optical path ofthe beam from the MO 452 to the PO chamber 442, which are drawnschematically to conform to the plane of the paper and not the opticalrealities of the optical path between the two and into the amplificationstage chamber 492.

The seed injection mechanism 300 may include, e.g., a partiallyreflective input/output coupler 302, e.g., a beam splitter similar tothose sold with applicants' assignee's laser systems, e.g., as part ofan optical pulse stretcher (“OPuS”), and a maximally reflective mirrorRmax 304 for the given nominal center wavelength, with the partiallyreflective output coupler 302 serving as an input/output coupler asnoted above and specifically as the output coupler for the ring poweramplification stage 490 oscillation cavity (defined also by the beamreverser 310). The seed laser output laser light pulse beam from the MO452 may pass into the ring power amplification stage chamber 492 throughan input window 500 and also pass through a beam expander 510 as notedabove with respect to FIG. 14. The input section 494 of the ring poweramplification stage chamber 492 may also house the beam expander 510,consisting of, e.g., a prism 512 and a prism 514. Other forms of seedinjection mechanisms may include those discussed in the above referencedco-pending provisional application filed on the same as the provisionalapplication from which this application claims priority and the otherco-pending applications claiming priority to that provisionalapplication or the provisional application from which this presentapplication claims priority.

The output of the ring power amplification stage oscillator 490 may bethe overall system output laser light pulse beam of laser pulses,however, as illustrated in FIG. 16, this beam (eventually output beam100 to the utilization tool, e.g., the scanner) passes also through ametrology unit (bandwidth analysis module “BAM”) 340, where output laserlight pulse beam bandwidth may be measured, e.g., for each pulse in thebeam, and through a pulse stretcher, e.g., a 4×OPuS 520 which mayinclude, e.g., a first delay path 522, which the laser system outputbeam enters through beam splitter 526 and a second delay path 524entered through beam splitter 528 (the delay paths formed by mirrors530). Leaving the OPuS 520 the output beam 100 passes through a shutter540 which may also have a beam splitter 542, e.g., to take off a portionof the laser system output laser light pulse beam 100 to measure, e.g.,pulse energy.

With the beam expander 170 in FIG. 3 and 142 in FIG. 2 placed inside thering power amplification stage oscillation cavity there is, e.g., areduction of the energy density on the maximum reflector 164 and partialreflector 162 that make up the input/output coupler 160 of the ringcavity of the amplification stage 180, 144 is achieved. With the beamreverser 70 moved to inside the cavity, the space vacated can house theBAM (or SAM). Need for optical coatings can be eliminated, e.g., due toreduced optical fluence on due to reduction of optical fluence, e.g., onthe input/output coupler partially reflecting mirror 162 and maximallyreflecting mirror 164, with the beam reverser 70 angled to reduceoptical damage, e.g., with an input and output at about Brewster's angleto reduce absorption and also to spread the beam on the input and outputfaces. There could also be no need protective coatings on theamplification stage chamber window 194,168. The output window 194, 168could be at a 47 degree orientation.

And also, since the power amplification stage reaches strong saturationwith 100 uJ of MO energy and below, e.g., down to about 5 μJ or so,output energy stability will be dominated by the good ring poweramplification stage characteristics and not the less than ideal MOenergy stability characteristics. The present Cymer XLA XXX MOPA systemsare dominated by the MO energy instabilities. Other output laser beamparameters, e.g., pointing stability, profile stability, and ASEstability may also be beneficially impacted by a configuration accordingto aspects of an embodiment of the disclosed subject matter utilizingreduced MO energy output.

According to aspects of an embodiment of the disclosed subject matterapplicants propose to use a 6 mirror coherency busting mechanism (forconvenience herein optical pulse delay paths are indicated schematicallyas having four mirrors per delay path) which has been developed byapplicants' assignee for additional path delay inside either or both ofthe 1^(st) or 2^(nd) pulse stretchers in the OPuS used with applicants'assignee's XLA model multi-chamber laser systems. Such a delay path can,e.g., produce −1 imaging with an odd number of imaging mirrors. This isillustrated schematically and in cartoon fashion, e.g., in FIGS. 37 and8 wherein is illustrated the summation of “flipped” sub-pulses. Theflipped sub-pulses shown, e.g., in FIG. 8 can be used, e.g., forimproved profile uniformity and symmetry and for overlapping into thedame output aperture pulses from different sources, e.g., as a beamcombiner.

It will be understood that the delay path for this coherency bustingpurpose need not be as long as the actual OPuS used for pulse stretchingto get a much increased pulse T_(is), and overlapping pulses. Rather thecoherency busting mechanism, a so-called “mini-OPuS”, among othercharacteristics can fold the pulses a certain number of times. This isillustrated by the pulse 580, with the corner (pre-flip) designated 582and the pulses 584, 586, 588. In addition, due to misalignment ofmirrors in the delay path, a “hall of mirrors” effect due to subportionsof the beam being misaligned, may also reduce the coherency in the seedlaser pulse, and, e.g., so long as the delay path exceeds the temporalcoherency length of the beam. In this regard, a four mirror mini-OPuS,e.g., with confocally arranged spherical mirrors for ease of alignment,may serve as a satisfactory coherency buster, even without beam flippingin both axis as explained elsewhere in this application. The basicrequirement is to mix the beam, e.g., by folding in on itself, in one ormore axes, i.e., whether or not negative one imaging occurs. Not onlycan this occur in OPuS like delay paths, or so-called mini-OPus likedelay paths, i.e., with imaging mirrors, but also in delay paths withflat mirrors, such that at least in every round trip of the delay pathdaughter pulses are flipped in at least one axis with respect to themain pulse and each other.

According to aspects of an embodiment of the disclosed subject matter itmay be necessary to combine two separate laser beams at various pointswithin a system according to aspects of an embodiment of the disclosedsubject matter. If only half of the entrance to a 6 mirror pulsestretcher is illuminated, the sub-pulses flip between top and bottom asshown, e.g., in FIG. 8. The summation of these “flipped” sub-pulses canlead to a filled in, full size profile, e.g., as illustrated in thepulse stretching simulation shown in FIG. 41, with the curve 562 showingthe pulse before entering the delay path and curve 564 (black) after onedelay path and 566 (red) after a second delay path. Laser divergence maythen be used to fill in the center portion 568, e.g., after somepropagation, e.g., over about 1 m or so.

Turning now to FIG. 40 there is shown a schematic representation of theeffects of coherence busting according to aspects of an embodiment ofthe disclosed subject matter. Utilizing an imaging delay path, e.g., apulse stretcher, e.g., a so-called optical pulse stretcher (“OPuS”),e.g., a 4×T_(is) four mirror OPuS sold with the above noted applicants'assignee's laser systems, and illustrated in U.S. Patents and co-pendingapplications noted above, or a modified version thereof with a shorterdelay, path used, e.g., for folding the beam on itself and/or for delayexceeding the coherence length as discussed herein, the so-calledmini-OPuS, one can achieve a degree of coherence busting, e.g., betweenthe MO and amplifier gain medium, e.g., a PA or a PO or a ring poweramplification stage. Other forms of coherence busting e.g., asillustrated in FIG. 31 could be used alone or in combination with such a“mini-OPuS,” e.g., as illustrated in FIG. 41 and elsewhere herein or asthe mini-OPuS itself.

According to aspects of an embodiment of the disclosed subject matter,the pointing/divergence, sensitivity of a pulse stretcher, e.g., a 4mirror or 6 mirror pulse stretcher, e.g., a regular OPuS such as a4×T_(is) OPuS, or a so-called mini-OPuS, or the delay path discussed inmore detail in regard to FIG. 31, and also including delay paths withsome or all mirrors being flat (non-imaging) can be put to advantage,e.g., by adding active mirror control with feedback from, e.g., apointing/divergence sensor; illustrated, e.g., in FIGS. 42 and 66. Suchadvantages include creating or sustaining, e.g., a hall of mirrorseffect whereby, e.g., the laser output light pulse beam being smoothedin the delay path actually becomes something like a plurality of beamsof very slightly different pointing and thus angle of incidence on thevarious mirrors of the pulse stretcher and/or down stream of the delaypath(s). Applicants assignee has observed this in pulse stretchers whereit is very difficult to perfectly align the mirrors, e.g., of thecurrently used 4×T_(is) OPuS pulse stretcher, thus creating the hall ofmirrors effect that reduces the coherence of the laser output lightpulse beam exiting the pulse stretcher. Thus the beam 860 a forms aplurality of separate beams 862 a.

FIG. 40 illustrates a reduction in coherency, e.g., when using both thereflectivity of an OC and an Rmax, e.g., in a flat-flat cavity with,e.g., a polarizing input coupling from a seed laser source of seed laserpulses. The angles have been exaggerated for clarity of illustration.There are, e.g., multiple rays produced by a static fan out, i.e., “hallof mirrors” effect, e.g., created between the OC and the Rmax. Thetheoretical energy weighting of these rays, assuming no transmissionlosses through the cavity and perfect reflectivity is shown below.

Ray Normalized Number Fractional Energy Energy 1 0.2 = 0.200 0.3125 20.8 * 0.8 = 0.640 1.000 3 0.8 * 0.2 * 0.8 = 0.128 0.2000 4 0.8 * 0.2 *0.2 * 0.8 = 0.0256 0.0400 5 0.8 * 0.2 * 0.2 * 0.2 * 0.8 = 0.00512 0.00806 0.8 * 0.2 * 0.2 * 0.2 * 0.2 * 0.8 = 0.00102 0.0016

One may assume that each ray is incoherent from all others, e.g., wherethe path length between the OC and the Rmax is maintained to be longerthan the temporal coherence length and, e.g., with non-overlappingstretching, i.e., of much less than the pulse length. Each ray may alsobe assumed, e.g., to be angled slightly different from all others since,e.g., perfect alignment is believed to be extremely difficult,especially in the vertical direction. Applicants believe that about 37μrad of angle difference in the vertical direction is needed to createuncorrelated speckle. Summing the normalized energy weighting to givethe equivalent number of independent pulses and taking the square rootto give the reduction in standard deviation, the sum from the above is1.56. The square root is 1.25 and thus the standard deviation when usingboth OC and Rmax reflections is predicted to be 0.551/1.25=0.440, whichcomports well with a value that applicants have measured, i.e., 0.427.

Static fan out, otherwise referred to herein as a hall of mirrorseffect, believed to be essentially unavoidable with manual alignment,produces a single pulse speckle contrast with amplification in anamplification gain medium that is 2.50× smaller than the seed laseralone. This reduction is the equivalent of 6.3 uncorrelated sub-pulses.Some of this contrast reduction is due to the weak line content from theXeF power oscillator used for testing the effects of the oscillationamplification stage, but most is believed to be due to the static fanout effect. Likely, many of the sub-pulses created by the OPuS-likestatic fan out characteristics of the OC-Rmax (OC-rear cavity mirror)reflections are all amplified to nearly equal intensities and thuscreate more equivalent independent pulses than shown in the above table.

In FIG. 40 this could also illustrate schematically the beam spreadingin, e.g., a flat-flat cavity 850 a with an input coupler, havingslightly misaligned mirrors forming the rear of the cavity 852 a and anoutput coupler 854 a, but the same effect has been observed in an OPuSby applicants employer with the coherence busting effect noted above.The cavity illustrated in FIG. 40 may also have a polarizing inputcoupler 858 a and a quarter wave plate 856 a.

Tilt angle required to produce uncorrelated speckle patterns may besignificant. The first big jump in equivalent pulses, from 1.0 to 1.55,is believed by applicants to be mostly due to the poor pulse-to-pulserepeatability of the speckle patterns when running as a MOPO. Evenwithout changing the mirror tilt at all, two pulses are correlated nobetter than 30-35%. With seed only, this pulse-to-pulse correlation hasbeen found to be about 85-90%. The long slow rise in equivalent pulsenumber does not even reach a value of 2.0 until about 400 μrad of mirrortilt as illustrated, e.g., in FIG. 37. This result could mean, e.g.,there may be a need for a large angular sweep, of about ±500-1000 μrad,e.g., to create several uncorrelated speckle patterns in a single pulse.

Through experimentation relating to coherence applicants' employer haslearned that, e.g., sub-pulses produced by a pulse stretcher areincoherent and lead to a different fringe pattern if their angles areslightly shifted, provided the sub-pulses are delayed by longer than thetemporal coherence length. The pin hole fringe pattern shifts maximum tominimum when input angle is λ/2 d.

Use of a solid state laser source for lithography has been proposed inthe past and not pursued for two reasons. Solid state lasers are notconsidered capable of the high average power required for lithographyand a solid state laser produces single mode output which is highly(perfectly) coherent. According to aspects of an embodiment of thedisclosed subject matter applicants propose to address the low averagepower problem with, e.g., a hybrid solid state seed/excimer amplifiercombination. The high coherence properties of the solid state seed canbe addressed in a number of ways according to aspects of embodiments ofthe disclosed subject matter, e.g., by creating sub-pulses, e.g., thatare separated in time longer than the coherence length along withchanging the seed laser pointing, e.g., over very short time scales,e.g., within a single laser pulse, or a combination of both. Coherencybusting has been found by applicants to be of benefit in dual chambergas discharge (e.g. excimer) seed/gas discharge (e.g., excimer)amplifier portion lasers as well.

It will be understood by those skilled in the art that an apparatus andmethod is disclosed for reaching very high average output power, e.g.,greater than 100 W or more with an excimer or molecular fluorine gasdischarge laser system in the DUV range of wavelengths, e.g., 351 forXeF, 318 for XeCl, 248 for KrF, 193 for ArF and 157 for F₂, utilizing,e.g., a power oscillator or other amplification gain stage, e.g., a ringpower amplification stage, with little or no significant ASE interferingwith the in-band desired radiation output of the laser system, e.g.,with a ratio between the ASE and in-band radiation at or below about5×10⁻⁴, e.g., with, e.g., a 100 uJ pulse energy input into the poweramplification stage cavity per pulse. According to aspects of anembodiment of the disclosed subject matter unwanted ring poweramplification stage light propagates backwards and can also be sampledfor diagnostics and ASE feedback control. Adding a small amount ofline-narrowing, e.g., with prism tuning, can also help suppress ASE fromthe power amplification stage. Also according to aspects of anembodiment of the disclosed subject matter a PA may be used, e.g., alongwith a solid state MO, e.g., a 4 pass amplifier with no oscillation butwith acceptable amplification and perhaps even high enough saturation.With such a design it may be necessary, e.g., for the 4 passes to eachtraverse the entire gain cross-section in each of the 4 passes. Thecavity may have 2 prisms on each side of the cavity, in order to, e.g.,reduce the energy density on the coated cavity optics and also providedispersion for ASE reduction.

In addition, it may not be that the ultimate ASE levels in a MOPO, orother master oscillator/power amplification stage configurations,necessarily increase with decreasing MO energy, such that according toaspects of an embodiment of the disclosed subject matter decreasing MOoutput energy even below 10 μJ may not result in unacceptable ASE, evenwithout, e.g., a partially reflective off axis seed injection mechanismand/or a regenerative ring power amplification stage configuration. Acavity with beam expansion and crossing beams may be constructed thatdoes not exceed the cavity length of today's XLA, e.g., with the beamexpansion prisms far enough away from the chamber to allow lateraltranslation for beam crossing, e.g., at a distance of a few centimetersof the chamber window, dictated by, e.g., beam width and crossing angle.A separate vessel for the prisms and/or beam reverser optics could alsoallow the use of a direct F₂ supply, e.g., at a different concentrationthan in the lasing gas mixture, e.g., at around 1% concentration. Thiscould also, e.g., avoid contamination from the optics holders.

The effect of inverse imaging, e.g., in an optical delay path, e.g., ina mini-Opus with a delay path of only about one foot, is illustrated inFIG. 37, e.g. for an input beam 580, in which a beam corner 582 isdesignated by the square initially in the lower right hand corner of thebeam 580 a. For a first sub-pulse 584, e.g., between an entrance beamsplitter and a first mini-OPuS mirror, the beam corner 582 remains thesame. In a second sub-pulse 586, e.g., reflected from the first mirror,the beam has been, e.g., negatively imaged, e.g., to a second mini-OPuSmirror and the beam corner has moved to the upper left hand corner andthen for a third sub-pulse 588, reflected to a fourth mini-OPus mirror,where the beam corner has been negatively imaged back to the bottomright hand corner, as illustrated in the figure. Combining all of thesesub-pulses into an output pulse, with a relatively short optical pulsedelay such that the pulse is not very significantly stretched from aT_(is) standpoint, can still substantially reduce coherency by thiseffect of folding the beam on itself a plurality of times, depending onthe number of mirrors in the delay path.

FIG. 8 illustrates this same effect, e.g., on half of the beam, e.g., isthe beam had been split into two halves before entry into the delay pathof, e.g., two separate sources, e.g., two solid state seed lasersoperating at X kHz in, e.g., a 2× kHz system. As can be seen the twohalves are similarly negatively imaged in each sub-pulse resulting ineven further reduction in coherency in an overall output pulse formed,e.g., by the combination of the two half pulses into a single outputpulse, e.g., of the shape shown by way of example in FIG. 37. as noted,this can also act as an effective beam combiner/mixer for combiningseparate beams from separate sources.

Turning now to FIG. 42 there is shown schematically and partly in blockdiagram form a beam combiner system 600 a, according to aspects of anembodiment of the disclosed subject matter. The beam combiner system 600a may include, e.g., a first amplifier gain medium portion 602 a and asecond amplifier gain medium portion 604 a, each of which may be, e.g.,a PA or PO of ring power amplification stage, as described elsewhere inthe present application. The output of each of the amplifier portions602 a, 604 a may pass through a beam expander 608 a, which may include aprism 610 a and a prism 612 a, e.g., magnifying the beam by, e.g., about2×. A turning mirror 620 a may steer a first laser system output lightpulse beam 622 a from the amplifier 602 a to a second turning mirror 624a which may steer the pulse beam 622 a to form a pulse beam 632 a onto abeam splitter for a first pulse stretcher 640 a and thence to a beamsplitter 646 a for a second pulse stretcher 644 a. A turning mirror 630a may steer a second laser system output light pulse beam 632 a from thesecond amplifier 604 a to a second turning mirror 634 a, which may steerthe beam 632 a to form a beam 634 a to be incident on the beam splitter642 a and thence the beam splitter 646 a. The output of the first OPuSand second OPuS, which may be “mini-OPuSs” as discussed elsewhere in thepresent application, may pass through another beam splitter 650 a,where, e.g., a small portion of the laser system output laser lightpulse beam may be diverted, e.g., for metrology purposes, e.g., focusedby a focusing lens 652 a into a divergence detector 654 a, which may bepart of a control system (not shown) providing feedback control signals656 a, e.g., to the beam splitters 642 a, 646 a of the first and/orsecond OPuSs 640 a, 644 a or the turning mirrors for each of the beams632 a, 634 a to, e.g., insure the pointing from both amplifiers remainoverlapped in the far field so that the beam appears to be as one beam,and also, e.g., so that the two pulse stretchers maintain the pointingchirp introduces=d, e.g., due to the confocal nature of the OPuS(s).

FIG. 38 illustrates schematically the impact of changing the pointing ofthe beam (sweeping the beam) in terms of coherency/speckle reduction. Apulse stretcher 662 may receive a laser system output laser light pulsebeam 100 on a beam splitter 664 and, e.g., through changing the angle ofthe beam splitter sweep the pointing of the beam 100 onto a diffuser670. The resultant detected speckle pattern 680 indicates that thesweeping reduces the coherency contrast and thus speckle.

Turning now to FIG. 66 there is illustrated by way of example inschematic and partly block diagram form a very high power solid stateseeded immersion lithography laser light source 1900, which may include,e.g., a high pulse repetition rate, e.g. a 12 kHz, solid state seedlaser 1902. The output of the seed laser 1902 may pass throughformatting optics 1904, which can include, e.g., a lens 1906 and a lens1908, which may be used to, e.g., to reformat the beam from a round beamto a shape concomitant with the shape of the gain medium in theamplifier portion. The output laser light pulse beam from the seed laser1902 may then be passed through an x axis electro-optical (“E-O”)steering mechanism 1912, and/or a y-axis E-O steering mechanism 1914 orboth, e.g., an E-O cell model referenced above, each providing, in arespective axis, e.g., orthogonal to each other, a sweep of the beam inorder to paint a reasonable percentage of the utilization tool (e.g.,scanner or annealing tool) aperture, e.g., about 1 mrad, along with ahigh frequency AC painting voltage, as explained elsewhere in thepresent application. The laser output light pulse beam pulses from theseed laser 1902 may then be split in a beam divider to providealternating (“tic-toc”) input pulses into a respective one of anamplifier gain medium, e.g., a first power oscillator 1930 a and asecond power oscillator 1930. The power oscillators 1930 and 1930 a maycomprise ring power oscillators.

The beam divider 1920 may comprise, e.g., a beam splitter 1922 thatselectively transmits, e.g., 50% of the output beam from the seed laser1902 onto a turning mirror 1924 and a turning mirror 1926, leading intothe second power oscillator 1930 and reflects 50% to a turning mirror1928 leading to the second power oscillator 1930, e.g., on each pulsethe beam splitter 1920 could also comprise, e.g., an electro-optical oracousto-optical beam deflector alternating actuated to send light tofolding mirror 1928 or folding mirror 1924 on alternate pulses.

Each respective power oscillator 1930 or 1930 a may include an inputcoupler/rear cavity mirror 1934, e.g., a concave mirror with an apertureon the axis of revolution of the mirror surface admitting the seed laserbeam into the cavity formed by the rear cavity mirror 1934 and a frontcavity mirror 1936 as are known in the art of unstable oscillationcavities. It will be understood that the amplifier gain medium may be inother configurations mentioned in the present application, e.g., astable resonator with, e.g., a seed injection mechanism, discussed inthe co-pending and contemporaneously filed application referenced above,and e.g., a ring power amplification stage, or a power amplifier,without an oscillator cavity and with only a fixed traversal path foramplification while the gain medium is energized (e.g., a populationinversion exists) as is known in the art, without laser oscillationoccurring, i.e., without an output coupler as is known in the art oflaser oscillation cavities. In oscillation cavity environments, e.g.,the convex mirrors could be replaced, e.g., by an input coupler such asthe seed injection mechanism, discussed in more detail elsewhere in thepresent application, and the convex mirror 1936 replaced with an outputcoupler. Beam expanding, beam combining and coherency busting anddivergence measuring (, e.g., where ASE is of concern) of the respectiveoutput beams 1966 from the first power oscillator 1930 a and 1964 fromthe power oscillator 1930, and feedback control may occur as discussedin regard to FIG. 21 with respective beam expander 1940, comprising,e.g., prisms 1942 and 1944, beam combiner comprising mirrors 1950, 1952from the first power oscillator 1930 a and mirrors 1960, 1962 from thesecond power oscillator 1930 and pulse stretchers 1840 and 1844 andmetrology unit 1854.

FIG. 39 illustrates schematically the results of a coherency bustingscheme on an output laser pulse, e.g., in relation to a scanneracceptance window, e.g., introducing horizontal and vertical (asillustrated in the plane of the page drawing of FIG. 39) directions. Thedot 780 a illustrated schematically and by way of example an initialseed laser output pulse profile 780 a. The pattern of pulses 782 aillustrate a pattern of sub-pulse profiles 782 a after beam folding in aperfectly aligned beam delay path, or through a misaligned pulsestretcher(s) or both, or a combination thereof, and the circles 784 aaround each represent the effect on the profile of electro-opticalsmearing.

FIG. 67 illustrates schematically and partly in block diagram form byway of example a ring power amplification stage oscillator laser system1800 and a seed injection mechanism 1812, as discussed in more detailherein. The laser system 1800 may comprise, e.g., a with bow-tie ringpower amplification stage 1804 and a seed laser, e.g., a solid state orgas discharge seed oscillator 1802. The seed oscillator 1802 may beisolated from the oscillator cavity of the power amplification stage1804 by an isolator to prevent unwanted lasing from feedback photons,which may be unnecessary, e.g., with a proper seed injection mechanism812. The power amplification stage section 1804 may include, e.g., apower amplification stage chamber 1810, a seed injection mechanism 1812,which may include, e.g., an input/output coupler 1814 and a maximallyreflective (“Rmax”) mirror 1816 beam reverser 1820, reflecting theoutput beam 1806 from the seed oscillator 1802 into the amplifierportion chamber 1804, and also include a beam reverser/returner 1820,which may include, e.g., a first maximally reflective mirror 1822 and asecond mirror 1824, e.g., made of a material, like the Rmax mirror 1816,selected to be maximally reflective for a suitable band around thenominal center wavelength of the laser system, e.g., 351 for XeF, 318for XeCl, 248 for KrF, 193 for ArF and 157 for F₂. The seed injectionmechanism and beam returner, as explained in more detail herein, may bearranged so as to form the oscillation cavity of the power amplificationstage 1840 (whether technically speaking an oscillator or amplifieroscillator stage, i.e., depending on cavity length). It will beunderstood that the angle of offset of the beams 826,828 is greatlyexaggerated for illustration purposes and could be around 1 μrad.

FIG. 68 illustrates schematically and partly in block diagram form asolid state seed/power amplifier laser system 1880 according to aspectsof an embodiment of the disclosed subject matter. The system mayincorporate a solid state 12 kHz seed laser 1882 and a pair of amplifiergain media, e.g., a pair of power amplifier chambers 1888. An opticalinterface module 1884 may receive the output of the seed laser 1882 anddirect it in tic-toc fashion into the respective amplifier gain medium1888, e.g., on alternating pulses. The optical interface module 1884 maycomprise, e.g., a pair of cylindrical telescopes 1886, which may serveto format the beam, e.g., because the output may be astigmatic with thetelescope serving to remove the astigmatism, and may also include, e.g.,an input optics module 1890, each including, e.g., a mirror 1902, amirror 1908 and a mirror 1910, which together with mirrors 1904 and 1906may form, e.g., a fixed number of passes, e.g., three passes through thegain medium between electrodes (not shown in FIG. 68) in an amplifiergain medium configured, e.g., as a three pass power amplifier (“PA”).that is, no laser oscillation occurs in the amplifier gain medium. Therespective outputs of the respective power amplifier 1888 may be steeredby beam turning mirror 1930, 1932 on the one hand and 1934, 1936 on theother through a respective energy sensor. These output beams from thesystem 1880 may be combined in a beam combiner as discussed elsewhere inthe present application.

A coherency buster, e.g., an automated two axis angular adjustmentmechanism 1910, e.g., modulating the tilt of the respective mirror 910in the input optics module 890 may serve a similar purpose to that ofthe X and Y axis beam steering electro optic elements 1712, 1714 of theembodiment of FIG. 66, e.g., by sweeping the beam entering the amplifiergain medium from side to side and/or up and down for greater divergenceand thus coherency busting as discussed elsewhere herein.

Turning now to FIG. 69 there is illustrates schematically and in partlyblock diagram format a seed laser/amplifier gain medium laser systemsuch as a solid state seed/power amplification stage laser system 1950according to aspects of an embodiment of the disclosed subject matter.The system 1950 may include, e.g., a seed laser, e.g., a solid state 12kHz seed laser 1952 the output of which may enter into an opticalinterface modules 1884, e.g., into a respective one of a pair ofcylindrical telescopes 1886, as in the embodiment of FIG. 68. Inputcoupling modules 1960 may include, e.g., a polarizing beam splitter1962, an Rmax 1964, a quarter wave plate 1966, and an input coupler Rmaxmirror 1968, which together function to couple output of the seed laser1952, respective seed beam 1970, 1972, into the respective gainamplifier medium, e.g., a power amplification stage oscillator having anoutput coupler 1982, by e.g., using a polarization coupling. Turningmirrors 1984, 1986, 1994, 1996 serve the same purpose as the respectiveturning mirrors in the embodiment of FIG. 68.

FIG. 70 represents an illustrative normalized MOPO intensity 1000, anormalized single pass PA intensity 1002 and a normalized two pass PAintensity 1004.

FIG. 71 represents an illustrative macroscopic steering pulse 1010,which may comprise a plurality of alternating high and low DC voltages1010, 0102, and 1014, which may repeat in some pattern, e.g., of threedifferent high voltages, as illustrated and a superimposed alternatingcurrent high frequency steering voltage 1016, which may occur, e.g.,both at the higher voltage and at the low voltage. As illustrated, e.g.,the high voltages may have different pulse durations and different lowvoltage duration intervals as well. As shown in FIG. 73, these highvoltages 1032 may be of the same value and same low voltage durationinterval 1036 with superimposed AC 1034.

FIG. 72 illustrates schematically and in block diagram form an opticalswitching and painting system 1020, according to aspects of anembodiment of the disclosed subject matter, which may include, e.g., asolid state seed 1022, a frequency converter 1024, and an optical switchand painter 1026, which may include an electro-optical beam directorthat, e.g., deflects the beam into a first one of an amplifier gainmedium 1030 when the pulse, e.g., as shown in FIG. 73 is high (1032 inFIG. 73 and into the other amplifier gain medium 1032, when the pulse islow (1036 in FIG. 73) and also applies the AC beam steering 1034 intoeach amplifier 1030, 1032. A second frequency shifter 1028 may beintermediate the beam splitter/painter 1026 and the respective amplifiergain medium 1032, and may be in addition to the frequency shifting ofthe element 1024 or in lieu thereof.

According to aspects of an embodiment of the disclosed subject matterapplicants propose to generate 193 nm laser light utilizing asolid-state seed laser, e.g., the generation of coherent 193 nmradiation in a solid-state configuration with a solid-state seed drivelaser (or lasers) that drive linear or nonlinear frequency conversionstages. One potential seed drive laser is the pulsed Yb fiber laser,lasing at around 1060 nm, tunable in the 1050-1080 nm region. Suchlasers constitute a mature and powerful fiber laser technology, whichmay, e.g., be configured to produce short temporal duration pulses (1-5ns) at multi-kilohertz repetition frequencies. To generate 193 nm using1060 nm as the longest wavelength mixing source, according to aspects ofan embodiment of the disclosed subject matter, applicants propose touse, e.g., sum frequency generation (“SFG”) with a long wavelength and amoderately short wavelength to generate deep ultraviolet (“DUV”). Secondharmonic generation (“SHG”) to reach 193 nm is not possible, due to thepresent lack of a 236.5 nm source as the other mixing wavelength.However, such a source could be derived by fourth harmonic generation,(“FHG”) of the 946 nm output of a q-switched diode-pumped Nd:YAG laser(946 nm being a lower efficiency transition in Nd:YAG.

The output of the Nd:YAG is essentially a fixed wavelength, and overalltunability could be provided by tuning the output wavelength of the Ybfiber laser, e.g., a Yb⁺³ fiber laser. Tunability of the Yb fiber laseroutput could be obtained via a CW diode seed laser, e.g., a New FocusVortex TLB-6021. Such a diode laser seeders can provide fast wavelengthcontrol over limited wavelength ranges, e.g., via internal PZT controlof reflectors, as desired for lithography source applications and have ahigh spectral purity. Nd:YAG lasers are operable at multi-kilohertzrepetition frequencies, ensuring the overall system repetition rate canmeet the repetition rate requirements for a practical excimer laserinjection seeding source.

To achieve narrow bandwidth operation, both laser sources needindividually to be narrowband. In Nd:YAG systems, this may be achieved,e.g., by injection seeding with a CW lower power Nd:YAG laser, e.g., ina non-planar ring oscillator architecture that is operating, e.g., witha single longitudinal mode output. In the Yb fiber laser case, thebandwidth could be assured via the CW diode laser seeder, whichtypically operates at very narrow linewidths, e.g., on the order of 100MHz FWHM. Further, appropriate large-mode area (“LMA”) fiber technologycould be used to minimize spectral degradation due, e.g., to nonlineareffects in the fiber comprising the fiber laser oscillator or anysubsequent amplification stages.

To generate 193.4 nm radiation, e.g., as illustrated schematically andpartly in block diagram form in FIG. 76, a system 1200 including, e.g.,a pulsed 946 nm Nd:YAG laser 1204 seeded by a 946 nm seed laser, e.g., a946 nm CW Nd:YAG seed laser 1202, which the output of the Nd:YAG laser1204 frequency doubled, in a frequency converter 1206, which mayinclude, e.g., a frequency doubler 1208, e.g., a non-linear materialsuch as an LBO or KTP crystal, followed by either another frequencydoubler (not shown) or a third harmonic generator 1210 and a fourthharmonic generator 1212 (e.g., each done using sum-frequency generationwith residual pump radiation, e.g., using the above noted crystals),either approach generating the fourth harmonic at 236.5 nm. The 236.5 nmradiation can then be mixed, e.g., in a sum frequency generation withthe 1060 nm output of the a Yb fiber laser in a final nonlinear crystalmixing stage, sum frequency generator 1240, e.g., a CLBO or a BBOcrystal. That is, e.g., 1/1040 (0.000943)+1/236.5 (0.00423)=1/193.3(0.005173). The fiber laser 1222 may have a rear oscillation cavitymirror 1224 and a front window 1226, with a Q-switch 1228.

CLBO is cesium lithium borate, which is an effective 4^(th) or 5^(th)harmonic generator for Nd:YAG output light, can be phase matched up for193 nm operation and has a damage threshold of >26 GW/cm². BBO is betabarium borate (b-BaB₂O₄), which is one of the most versatile nonlinearoptical crystal materials available and most commonly used for second-or higher-order harmonic generation of Nd:YAG, Ti:Sapphire, argon ionand alexandrite lasers. CLBO may be used, e.g., because of its highertransparency and high acceptance angle, which may, however, requirecryogenic cooling for phase matching, also being problematic becauseCLBO is a hygroscopic material). An alternative is, e.g., BBO, which canbe phase matched but is being operated very close to its absorption bandedge at ˜190 nm. BBO also has much a narrower acceptance angle thanCLBO, but this can be managed through optical design, e.g., withanamorphic focusing. According to aspects of an embodiment of thedisclosed subject matter both lasers 1024, 1022 can be made relativelypowerful, e.g., with real output power of greater than about 25 KW,helping to compensate for any inefficiencies in the nonlinear frequencyconversion stages 1206, 1240.

According to aspects of the disclosed subject matter, the generation of193.3 nm with solid state laser(s) for seeding an excimer amplifier gainmedium may also be done, e.g., by the use of mature drive lasertechnologies, which may be wavelength tunable in a similar fashion tocurrent tuning of excimer lasers. A seed laser system 1200′, illustratedschematically and in partly block diagram form in FIG. 77, may comprise,e.g., an Er fiber laser 1260, e.g., lasing at around 1550 nm but tunablein the 1540-1570 nm range. Er fiber lasers are available, and usesimilar generic technologies to Yb fiber lasers. Such an approach isattractive because of the maturity of fiber and pump diode lasertechnology for this wavelength range, applied, e.g., in fiber-basedtelecommunications, e.g., erbium-doped fiber amplifiers or EDFAs used assignal boosters in optical fiber communication.

According to aspects of an embodiment of the disclosed subject matterapplicants propose to use a pulsed fiber laser oscillator 1260 as thesource of moderate peak power (e.g., 5-50 kW) high-repetition-rate(multi-kHz, e.g., at least 12) 1546.5 nm narrowband pulsed radiation.That laser 1260 could be constructed using standard pulsed fiber lasertechnology, to use a single-mode CW tunable narrowband diode laser 1262as an injection seeder for the fiber laser oscillator 1260 to ensurenarrowband, single wavelength performance, and also to allow the fastwavelength tunability required for lithography light sourceapplications. An example of the type of diode laser seeder 1262 is,e.g., a New Focus Vortex TLB-1647, which uses an external cavity diodeconfiguration with PZT wavelength actuation for high-speed wavelengthdrive over a limited wavelength range, in parallel with mechanical drivefor extended wavelength range operation. Further, appropriate large-modearea (“LMA”) fiber technology could be used to minimize spectraldegradation, e.g., due to nonlinear effects in the fiber comprising thefiber laser oscillator or any subsequent amplification stages. Usingsuch approaches can, e.g., allow spatial beam quality to be maintained,employing techniques for ensuring single-mode operation in large modearea fibers, while reducing the peak power in the core of the fiber.After the 1546.5 nm radiation is generated, it may then be frequencyupconverted directly to 193.3 nm, e.g., using five stages of nonlinearfrequency conversion, either second harmonic generation, or sumfrequency generation. This can be achieved through the steps listed inFIG. 78, one of which is illustrated by way of example in FIG. 77,wherein co refers to 1546.5 nm and 8ω becomes 193.3 nm. In FIG. 77 thereis shown the generation of the second harmonic 2ω of 1546.5 nm in SHG1208, and the third harmonic generation, e.g., by adding the basefrequency to the second harmonic to in SFG 1258 to get 3ω, and frequencydoubling 3 W to get 6ω in frequency double 1258, followed by similarsuch sum frequency generations as just noted in SFGs 1252 and 1254 toget, respectively, 7ω and 8ω. In addition, according to aspects of anembodiment of the disclosed subject matter relatively low-power pulsedfiber laser oscillator outputs, e.g., seeded by a diode laser forspectrum/wavelength control, could then be boosted in peak power via,e.g., a subsequent stage(s) of fiber amplification (not shown).Applicants propose also, the development of an all-fiber solid statedrive laser based on this approach.

Turning to FIG. 47 there is illustrated schematically and in blockdiagram form a laser treatment system, e.g., and LTPS or tbSLS laserannealing system, e.g., for melting and recrystallizing amorphoussilicon on sheets of glass substrates at low temperature. The system1070 may include, e.g., a laser system 20 such as described herein and aoptical system 1272 to transform the laser 20 output light pulse beamfrom about 5×12 mm to 10 or so microns×390 mm or longer thin beams fortreating a workpiece, e.g., held on a work piece handling stage 1274.

MO/amplification stage energy vs. MO/amplification stage timing has beenexamined at different values of seed laser energy, ArF chamber gasmixture, percentage reflectivity of output coupler (cavity Q) and seedlaser pulse duration, with the results as explained in relation to FIG.7.

ASE vs. MO/amplification stage timing has been examined for differentvalues of seed laser energy, ArF chamber gas mixture, percentagereflectivity of output coupler (cavity Q) and seed laser pulse durationwith the results also explained in relation to FIG. 7.

Turning to FIG. 7 there is shown a chart illustrating by way of examplea timing and control algorithm according to aspects of an embodiment ofthe subject matter disclosed. The chart plots laser system output energyas a function of the differential timing of the discharge in the seedlaser chamber and the amplification stage, e.g., the ring poweramplification stage as curve 600, which is referred to herein as dtMOPOfor convenience, recognizing that the amplification stage in someconfigurations may not strictly speaking be a PO but rather a PA thoughthere is oscillation as opposed to the fixed number of passes through again medium in what applicants' assignee has traditionally referred toas a power amplifier, i.e., a PA in applicants' assignee's MOPA XLA-XXXmodel laser systems, due, e.g., to the ring path length's relation tothe integer multiples of the nominal wavelengths. Also illustrated is arepresentative curve of the ASE generated in the amplification stage ofthe laser system as a function of dtMOPO, as curve 602. In additionthere is shown an illustrative curve 604 representing the change in thebandwidth of the output of the laser system as a function of dtMOPO.Also illustrated is a selected limit for ASE shown as curve 606.

It will be understood that one can select an operating point on thetiming curve at or around the minimum extremum of ASE and operate there,e.g., by dithering the control selection of dtMOPO to, e.g., determinethe point on the operating curve 602 at which the system is operating.It can be seen that there is quite a bit of leeway to operate around theminimum extremum of the ASE curve 602 while maintaining output pulseenergy on the relatively flat top portion of the energy curve to, e.g.,maintain laser system output pulse energy and energy σ, and the relateddose and dose σ constant, within acceptable tolerances. In addition asshown, there can be a concurrent use of dtMOPO to select bandwidth froma range of bandwidths while not interfering with the E control justnoted.

This can be accomplished regardless of the nature of the seed laserbeing used, i.e., a solid state seed or a gas discharge laser seed lasersystem. Where using a solid state seed laser, however, one of a varietyof techniques may be available to select (control) the bandwidth of theseed laser, e.g., by controlling, e.g., the degree of solid state seedlaser pumping or any of a number of means well known in the art. Suchpump power control may, e.g., put the pumping power at above the lasingthreshold in order to select a bandwidth. This selection of bandwidthmay shift or change the pertinent values of the curve 604, but the lasersystem will still be amenable to the type of E and BW control notedabove using dtMOPO to select both a BW and concurrently an operatingpoint that maintains the output energy of the laser system pulses at astable and more or less constant value in the flat top region of theillustrated energy curve 600. It is also possible to use a non-CW solidstate seed laser and to adjust the output bandwidth. For example,selection of the output coupler reflectivity of the master oscillatorcavity (cavity-Q) can adjust the output bandwidth of the seed lasersystem. Pulse trimming of the seed laser pulse may also be utilized tocontrol the overall output bandwidth of the laser system.

It can be seen from FIG. 7 that either the selected ASE upper limit orthe extent of the portion of the energy curve that remains relativelyflat with changes in dtMOPO may limit the range of available bandwidthfor selection. The slope and position of the BW curve also can be seento influence the available operating points on the timing curve tomaintain both a constant energy output and a minimum ASE while alsoselecting bandwidth from within an available range of bandwidths by useof the selection of a dtMOPO operating value.

It is similarly known that the pulse duration of discharge pulses in agas discharge seed laser, among other things, e.g., wavefront controlmay be used to select a nominal bandwidth out of the seed laser and thusalso influence the slope and/or position of the BW curve 604 asillustrated by way of example in FIG. 7.

According to aspects of an embodiment of the subject matter disclosedone may need to select an edge optic that is an optic that may have tobe used, and thus perhaps coated, all the way to its edge, which can bedifficult. Such an optic could be required, e.g., between the outputcoupler, e.g., 162 shown in FIG. 2 and the maximum reflector, e.g., 164,shown in FIG. 2, together forming a version of a seed injectionmechanism 160, shown in FIG. 2, e.g., depending upon the separationbetween the two, since there may be too little room to avoid using anedge optic. If so, then the edge optic should be selected to be theRmax, e.g., because of the ray path of the exiting beam as it passesthrough the OC portion 162. From a coatings standpoint it would bepreferable to have the OC be the edge optic because it has fewer layers.However, an alternative design, according to aspects of an embodiment ofthe subject matter disclosed has been chose by applicants and isillustrated schematically and by way of example in FIG. 30, e.g.,wherein the use of an edge optic can be avoided, e.g., if a large enoughspacing is provided between out-going and in-coming ring poweramplification stage beams, e.g., as created by the beam expander, 142shown in FIG. 2, e.g., prisms 146, 148. For example, about a 5 mmspacing between the two beams has been determined to be satisfactoryenough to, e.g., to avoid the use of any edge optics.

As illustrated by way of example in FIG. 46 the laser system, e.g.,system 110 illustrated by way of example in FIG. 2, may produce a lasersystem output pulse beam 100, e.g., using a ring power amplificationstage 144 to amplify the output beam 62 of a master oscillator 22 in aring power amplification stage 144. A beam expander/disperser 142, shownin more detail by way of an example of aspects of an embodiment of thesubject matter disclosed may be comprised of a firstexpansion/dispersion prism 146 a, and a second expansion/dispersionprism 146 b, and a third prism 148.

The seed injection mechanism 160 may comprise a partially reflectiveinput/output coupler 162, and a maximally reflective (Rmax) mirror 164,illustrated by way of example and partly schematically in FIG. 30 in aplan view, i.e., looking down on the seed injection mechanism and mexpansion/dispersion 160 and the ring power amplification stage chamber(not shown) into and out of which, respectively the beams 74 and 72traverse, that is from the perspective of the axis of the output beam 62traveling from the master oscillator chamber 22, which in such anembodiment as being described may be positioned above the chamber 144(the beam 62 having been folded into the generally horizontallongitudinal axis as shown (the beam also having been expanded in theMOPuS (also called the MO WEB, having the mini-OPuSs and a beam expanderas discussed elsewhere) in its short axis, as described elsewhere, tomake it generally a square in cross-sectional shape.

With regard to the configuration of the beam expansion prisms 146 a, 146b and 148 inside the ring power amplification stage cavity a similararrangement may be provided to that of the beam expansion on the outputof the power amplifier (“PA”) stage in applicants' assignee's XLA-XXXmodel laser systems, e.g., with a 4× expansion, e.g., provided by a68.6° incident and 28.1° exit, e.g. on a single prism or on two prismswith the same incident and exit angles. This can serve to, e.g., balanceand minimize the total Fresnel losses. Reflectivity coatings, e.g.,anti-reflectivity coatings may be avoided on these surfaces since theywill experience the highest energy densities in the system. According toaspects of an embodiment of the subject matter disclosed the beamexpander/disperser 160 may be implemented with the first prism 146 splitinto to small prisms 146 a, and 146 b, which may be, e.g., 33 mm beamexpander prisms, e.g., truncated, as shown by way of example in FIG. 30,to fit in the place where one similarly angled prism could fit, with thesplit prism having a number of advantages, e.g., lower cost and theability to better align and/or steer the beams 72, 74 (in combinationwith the beam reverser (not shown in FIG. 30) and the system output beam100.

The master oscillator seed beam 62 may enter the seed injectionmechanism 160 through the beam splitter partially reflective opticalelement 162, acting as an input/output coupler, to the Rmax 164 as beam62 a, from which it is reflected as beam 74 a to the first beam expanderprism 146 a, which serves to de-magnify the beam in the horizontal axisby about ½× (it remains about 10-11 mm in the vertical axis into theplane of the paper as shown in FIG. 30). The beam 74 b is then directedto the second beam expansion prism 148, e.g., a 40 mm beam expansionprism, where it is again de-magnified by about ½× so the totalde-magnification is about ¼× to form the beam 74 entering the gainmedium of the ring power amplification stage (not shown in FIG. 30. thebeam is reversed by the beam reverser, e.g., a beam reverser of the typecurrently used in applicants' assignee's XLA-XXX model laser system PAsand returns as beam 72 to the prism 148, e.g., having crossed in thegain medium in a bow-tie arrangement or having traveled roughlyparallel, perhaps overlapping to some degree in a version of arace-track arrangement. from prism 148 where the beam 72 is expanded byroughly 2× the beam 72 b is directed to prism 142 b and is expanded afurther approximately 2× into beam 72 a. Beam 72 a is partiallyreflected back to the Rmax as part of beam 62 a and is partiallytransmitted as output beam 100, which gradually increases in energyuntil an output beam pulse of sufficient energy is obtained by lasingoscillation in the ring power amplification stage. The narrowing of thebeam entering the amplification gain medium, e.g., the ring poweramplification stage has several advantageous results, e.g., confiningthe horizontal widths of the beam to about the width of the electricalgas discharge between the electrodes in the gain medium (for a bow-tiearrangement the displacement angle between the two beams is so smallthat they each essentially stay within the discharge width of a few mmeven thought they are each about 2-3 mm in horizontal width and for therace track embodiment, the beam 72 or the beam 72 only passes throughthe gain medium on each round trip, or the beams may be furthernarrowed, or the discharge widened.

The positioning and alignment of the prisms 146 a, 146 b and 148,especially 146 a and 146 b can be utilized to insure proper alignment ofthe output beam 100 from the ring power amplification stage into thelaser output light optical train towards the shutter. The beam leavingthe input/output coupler 162 may be fixed in size, e.g., in thehorizontal direction, e.g., by a horizontal size selection aperture 130,forming a portion of the system aperture (in the horizontal axis) toabout 10.5 mm. Another aperture, e.g., in the position roughly of thepresent PA WEB, e.g., in applicants' assignee's XLA-XXX laser systemproducts, can size the beam in the vertical dimension. since the beamhas about a 1 mRad divergence, the sizing may be slightly smaller ineach dimension than the actual beam dimensions wanted at the shutter,e.g., by about 1 mm. According to aspects of an embodiment of thesubject matter disclosed applicants propose that a system limitingaperture be positioned just after the main system output OPuS, e.g., a4×OPus. A ring power amplification stage aperture may be located about500 mm further inside the laser system. This distance is too great toavoid pointing changes turning into position changes at the specifiedmeasurement plane (present system aperture). Instead the limiting systemaperture can be located just after the OPuS, and may have a 193 nmreflecting dielectric coating instead of a stainless steel platecommonly used. This design can allow for easier optical alignment, whileat the same time reduce heating of this aperture.

According to aspects of an embodiment of the subject matter disclosed,applicants propose to implement a relatively stress-free chamber windowarrangement similar to or the same as that discussed in an abovereferenced co-pending U.S. patent application, e.g., at least on thebean reverser side of the chamber, because of the use of, e.g., a PCCFcoated window a this location.

According to aspects of an embodiment of the subject matter disclosed,applicants propose to, e.g., place ASE detection, e.g., backwardpropagation ASE detection, in either the LAM or in an MO wavefrontengineering box (“WEB”), or the so-called MOPuS, which can, e.g.,include elements of the MOWEB from applicants' assignee's existingXLA-XXX model laser systems along with the mini-OPuSs discussedelsewhere in this application, as well as, e.g., beam expansion, e.g.,using one or more beam expansion prisms to expand the output beam of theMO in its short axis, e.g., to form generally a square cross-sectionalbeam. The current MO WEB and its beam turning function is representedschematically as the turning mirror, e.g., 44 shown in FIG. 2. As apreference, however, the backward propagation detector may be placed“in” the MO WEB/MOPuS, that is, e.g., by employing a folding mirror(fold #2), e.g., 44 in FIG. 2, with, e.g., a reflectivity of R=95%instead of R=100% and monitoring the leakage through this mirror 44.Some drift and inaccuracy of this reading may be tolerated, e.g., sinceit may be utilized as a trip sensor (i.e. measurements in the vicinityof 0.001 mJ when conditions are acceptable—essentially no reverse ASE—asopposed to around 10 mJ when not acceptable—there is reverse ASE), e.g.,when the ring power amplifier is not timed to amplify the seed pulse,but still creates broad band laser light. Existing controller, e.g., TEMcontroller, cabling and ports and the like for new detectors may beemployed. The detector may, e.g., be the detector currently used byapplicants' assignee on existing XLA-XXX model laser systems to measurebeam intensity, e.g., at the laser system output shutter.

According to aspects of an embodiment of the disclosed subject matterone or more mini-OPuS(s), which may be confocal, such that they arehighly tolerant to misalignment and thus of potentially low aberration,e.g., for the off-axis rays needed in the proposed short OPuS(s), theso-called mini-OPuS, can have delay times of 4 ns and 5 ns respectively,where more than one is employed. These values were chosen so that bothOPuSs exhibit low wavefront distortion with spherical optics in additionto appropriate delay paths for coherence busting. The low wavefrontrequirement may actually prevent significant speckle reduction from themini-OPuS(s) unless special means are utilized, e.g., an angular fan-outfrom the output of the mini-OPuS(s) generated, e.g., by replacing aflat/flat compensating plate with a slightly wedged plate, so that thetransmitted beam and the delayed beam in the mini-OPuS are slightlyangularly offset from each other. Other means may be employed, e.g.,beam flipping in either or both axes, e.g., top to bottom or left toright, negative one imaging, the combination of top to bottom and leftto right flipping, and beam translation (shear), which may beaccomplished, e.g., by removing the compensator plate such as is shownin the co-pending patent application noted above entitled CONFOCAL PULSESTRETCHER, Ser. No. 11/394,512, filed on Mar. 31, 2006, or the additionof a second compensator plate in a second axis, e.g., orthogonal to thatof the first.

The laser beam, e.g., from the master oscillator is partially coherent,which leads to speckle in the beam. Angularly offsetting the reflectedbeam(s) reentering the mini-OPuS output with the transmitted beam, alongwith the delay path separation of the main pulse into the main pulse anddaughter pulses, can achieve very significant speckle reduction, e.g.,at the wafer or at the annealing workpiece, arising from the reductionin the coherence of the laser light source pulse illuminating theworkpiece (wafer or crystallization panel). This can be achieved, e.g.,by intentionally misaligning the delay path mirrors, probably notpossible with a confocal arrangement, but also with the addition of aslight wedge in the delay path prior to the beam splitter reflectingpart of the delayed beam into the output with the transmitted beam andits parent pulse and preceding daughter pulses, if any. For example, a 1milliradian wedge in the plate will produce an angular offset in thereflected daughter pulse beam of 0.86 milliradians.

The optical delay path(s) of the mini-OPuS(s) may have other beneficialresults in terms of laser performance and efficiency. According toaspects of an embodiment of the disclosed subject matter, as illustratedschematically in FIG. 48, the laser beam, e.g., seed beam 500 from theseed source laser (not shown in FIG. 48, may be split into two beams502, 504 using a partially reflective mirror (beam splitter) 510. Thismirror 510 transmits a percentage of the beam into the main beam 502 andreflects the rest of the beam 500 as beam 504 into an optical delay path506. The part 502 that is transmitted continues into the rest of thelaser system (not shown in FIG. 48). The part 504 that is reflected isdirected along a delay path 506 including, e.g., mirrors 512, 514 and516, with mirror 514 being displaced perpendicularly to the plane of thepaper in the schematic illustration, in order to allow the main beam 502to reenter the rest of the laser system, e.g., to form a laser outputbeam or for amplification in a subsequent amplification stage. The beam504 may then be recombined with the transmitted portion 502 of theoriginal beam 500. The delayed beam 504 may be passed through a wedge(compensator plate) 520 essentially perpendicularly arranged in the pathof beam 504. Thus, the daughter pulse beam(s) 504 from the delay path506 are slightly angularly displaced from the main part of the beam inthe transmitted portion 502 in the far field. The displacement may be,e.g., between about 50 and 500 μRad.

The length of the delay path 506 will delay the beam pulses so thatthere is a slight temporal shift between the part of the beam that istransmitted and the part that is reflected, e.g., more than thecoherence length, but much less than the pulse length, e.g., about 1-5ns. By selecting the appropriate path length, which determines the delaytime, the addition of the two beams can be such that the energy in thepulse is spread into a slightly longer T_(is) which in combination withlater pulse stretching in the main OPuS(s) can improve laserperformance, as well as providing other beneficial laser performancebenefits.

Two mini-OPuSs may be needed to achieve the desired effect. The offsettime between the pulses from the two mini-OPuSs may be, e.g., 1-2nanosecond. Based upon optical and mechanical considerations, the delaysselected for the stretchers may be, e.g., a 3 ns delay path in the firstmini-OPuS and a 4 ns delay path in the second. If the delay is shorter,the optical system, e.g., if it uses confocal or spherical mirrors, canintroduce unacceptable aberrations. If the delay is longer, it may bedifficult to fit the system into the available space in the lasercabinet. The distance the beam must travel to achieve the 3 ns delay is900 mm and to delay by 4 ns is 1200 mm. A confocal optical system 500,minimizing the sensitivity to misalignment, illustrated schematically inFIG. 49 may consist of two mirrors 522, 524, whose focal points arelocated at the same position in space and whose center of curvatures arelocated at the opposite mirror, along with a beam splitter 526. Acompensator plate 530 (e.g., a wedge) can be added to insure that thereflected beam and the transmitted beam are slightly misaligned as notedabove with respect to FIG. 49. In this case, the compensator plate isplaced in the path of the delayed beam at an angle for properfunctioning.

The delay path time(s) in the mini-OPuS(s) for coherence busting andother purposes may be as short as about the temporal coherence lengthand as long as practical due to the noted optical and spaceconsiderations, such as misalignment and aberration tolerance. If thereare two or more mini-OPuSs then the delay path in each must be differentin length, e.g., by more than the coherence length and selected suchthat there is no significant coherence reaction (increase) due to theinteraction of daughter pulses from the separate OPuS(s). For examplethe delay path times could be separated by at least a coherence lengthand by not more than some amount, e.g., four or five coherence lengths,depending on the optical arrangement.

According to aspects of an embodiment of the subject matter disclosedapplicants propose to employ a coherence-busting optical structure that,e.g., generates multiple sub-pulses delayed sequentially from a singleinput pulse, wherein also each sub-pulse is delayed from the followingsub-pulse by more than the coherence length of the light, and inaddition with the pointing of each sub-pulse intentionally chirped by anamount less than the divergence of the input pulse. In additionapplicants propose to utilize a pair of coherence-busting optical delaystructures, where the optical delay time difference between the pair ofoptical delay structures is more than the coherence length of the inputlight. Each of the two optical delay structures may also generatesub-pulses with controlled chirped pointing as noted in regard to theaspects of the previously described coherence busting optical delaystructure.

According to aspects of an embodiment of the disclosed subject mattertwo imaging mini-OPuSs, which may be confocal, such that they are highlytolerant to misalignment and thus of potentially low aberration, e.g.,for the off-axis rays needed in the proposed short OPuSs, the so-calledmini-OPuSs, and can have delay times of 4 ns and 5 ns respectively.These values were chosen so that both OPuSs exhibit low wavefrontdistortion with spherical optics. The low wavefront requirement mayprevent significant speckle reduction from the mini-OPuSs unless specialmeans are utilized, e.g., an angular fan-out, or a positiontranslation/shear (“position chirp”) or beam flipping/inversion as notedabove, from the mini-OPuSs is generated, e.g., by replacing a flat/flatcompensating plate with a slightly wedged plate or adding anothercompensation plate in a different axis.

It will be understood by those skilled in the art that according toaspects of an embodiment of the disclosed subject matter, adequatecoherence busting may be achieved sufficiently to significantly reducethe effects of speckle on the treatment of a workpiece being exposed toillumination from the laser system, such as in integrated circuitphotolithography photoresist exposure (including the impact on line edgeroughness and line width roughness) or laser heating, e.g., for laserannealing of amorphous silicon on a glass substrate for low temperaturerecrystallization processes. This may be accomplished by, e.g., passingthe laser beam, either from a single chamber laser system or from theoutput of a multi-chamber laser system or from the seed laser in such amulti-chamber laser system before amplification in another chamber ofthe multi-chamber laser system, through an optical arrangement thatsplits the output beam into pulses and daughter pulses and recombinesthe pulses and daughter pulses into a single beam with the pulses anddaughter pulses angularly displaced from each other by a slight amount,e.g., between, e.g., about 50 μRad and 500 μRad and with each of thedaughter pulses having been delayed from the main pulse(s), e.g., by atleast the temporal coherence length and preferably more than thetemporal coherence length.

This may be done in an optical beam delay path having a beam splitter totransmit a main beam and inject a portion of the beam into a delay pathand then recombining the main beam with the delayed beam. In therecombination, the two beams, main and delayed, may be very slightlyangularly offset from each other (pointed differently) in the far field,referred to herein as imparting a pointing chirp. The delay path may beselected to be longer than the temporal coherence length of the pulses.

The angular displacement may be accomplished using a wedge in theoptical delay path prior to the delayed beam returning to the beamsplitter which wedge imparts a slightly different pointing to thedelayed beam (a pointing chirp). The amount of pointing chirp, as notedabove may be, e.g., between about 50 and 500 μRad.

The optical delay paths may comprise two delay paths in series, eachwith a respective beam splitter. In such an event each delay path can bedifferent in length such that there is not created a coherence effectbetween the main and daughter pulses from the respective delay paths Forexample, if the delay in the first delay path is 1 ns the delay in thesecond delay path could be about 3 ns and if the delay in the firstdelay path is 3 ns the delay in the second could be about 4 ns.

The wedges in the two separate delay paths may be arranged generallyorthogonally to each other with respect to the beam profile, such thatthe wedge in the first delay path can serve to reduce coherence(speckle) in one axis and the wedge in the other delay path can reducecoherence (speckle) in the other axis, generally orthogonal to thefirst. thus, the impact on speckle, e.g., contribution to line edgeroughness (“LER”) and/or line width roughness (“LWR”), e.g., at thewafer in exposure of photoresist in an integrated circuit manufacturingprocess can be reduced along feature dimensions in two different axes onthe wafer.

Other special means as noted above, e.g., beam translation, beamimaging, fan-out flipping and the like may be employed.

According to aspects of an embodiment of the subject matter disclosed,with, e.g., a 6 mrad cross of the bowtie in a bowtie ring poweramplification stage, the magnification prisms inside the ring cavity maybe slightly different for the in-going and outgoing beams, and could bearranged so that the beam grows slightly as it travels around the ringor shrinks slightly as it travels around the ring. Alternatively, andpreferably according to aspects of an embodiment of the subject matterdisclosed, a result of breaking the larger beam expansion prism into twoseparate pieces, e.g., enabled by larger spacing between out-going andin-coming beams, e.g., about 5-6 mm, as illustrated by way of example inFIG. 30, applicants propose to adjust the angles of the two prisms,e.g., 146, 148 shown schematically in FIG. 4, such that they result inthe same magnification for both out-going and in-coming beams, e.g.,beams 100 and 62, respectively, shown illustratively and schematicallyin FIG. 30.

According to aspects of an embodiment of the subject matter disclosedapplicants propose to place the Rmax, e.g., 164 and the OC, e.g., 162portions of the version of the seed injection mechanism containing anRmax 164 and an OC 162, e.g., along with the positioning of the systemhorizontal axis beam output aperture on that same stage. This enables,e.g., prior alignment of each as an entire unit and removes the need forfield alignment of the individual components. This can allow, e.g., forthe position of the Rmax/OC assembly, e.g., 160, shown in FIG. 2 (a seedinjection mechanism) to be fixed, just like the OC location in aapplicants' assignee's single chamber oscillator systems (e.g., XLS 7000model laser systems) is fixed. Similarly, such an arrangement can allowfor the achievement of tolerances such that the Rmax/OC are positionedrelative to the system aperture properly without need for significantongoing adjustment. The beam expansion prism may be moveable foralignment of the injection seed mechanism assembly with the chamber 144of the amplification gain medium and the output beam 100 path with thelaser system optical axis.

According to aspects of an embodiment of the subject matter disclosedapplicants propose to employ a coherence-busting optical structure thatgenerates multiple sub-pulses delayed sequentially from a single inputpulse, wherein also each sub-pulse is delayed from the followingsub-pulse by more than the coherence length of the light, and inaddition with the pointing of each sub-pulse intentionally chirped by anamount less than the divergence of the input pulse, or any of the otherspecial means noted above. In addition applicants propose to utilize apair of coherence-busting optical delay structures, where the opticaldelay time difference between the pair of optical delay structures ismore than the coherence length of the input light. Each of the twooptical delay structures may also generate sub-pulses with controlledchirped pointing as noted in regard to the aspects of the previouslydescribed coherence busting optical delay structure, or any of the otherspecial means noted above.

According to aspects of an embodiment of the subject matter disclosedapplicants propose to position a mechanical shutter to block the MOoutput from entering the ring, when appropriate, similar to such as areutilized on applicants' assignee's OPuSs, e.g., to block them duringalignment and diagnosis. The exact location could be, e.g., just abovethe last folding mirror prior to the ring power amplification stage,where the mini-OPuSes are protected during unseeded ring poweramplification stage alignment and operation.

Turning now to FIG. 79 there is shown schematically and in block diagrama laser DUV light source according to aspects of an embodiment of thedisclosed subject matter. The system 1300 may include, e.g., a pluralityof seed laser systems, which may be solid state lasers, 1302, 1304,1306, for example as described elsewhere in the present application,with the seed laser 1306 being an nth seed laser in the system. for eachseed laser there may be a corresponding amplification laser system,e.g., 1310, 1320 and 1330, with the amplification laser system 1306being an nth amplification laser system. each amplification laser system1310, 1320, 1330 may have a plurality of A, in the illustrative caseA=2, amplification gain mediums 1312, 1314, and 1322, 1324 and 1332,1334, with the amplification gain mediums 1332, 1334 comprising anexemplary nth amplification gain medium system 1330. Each gain medium1312, 1314, 1322, 1324, 1332, 1334 may comprise a gas discharge laser,such as an excimer or molecular fluorine laser, and more specificallymay comprise a ring power amplification stage as described elsewhere inthe present application and in above identified co-pending applicationsfiled on the same day as the present application. Each of the respectiveA amplification gain mediums 1312, 1314 and 1322, 1324 and 1332, 1334may be supplied with output pulses from the respective seed laser 1302,1304 and 1306 by a beam divider 1308. The respective amplifier gainmediums 1312, 1314, 1322, 1324 and 1332, 1334 may operate at a fractionof the pulse repetition rate X of the respective seed lasers, e.g., A/X.A beam combiner 1340 may combine the outputs of the amplifier gainmediums 1312, 1314, 1322, 1324, 1332, 1334 to form a laser system 1300output laser light source beam 100 of pulses at a pulse repetition rateof nX.

Turning to FIG. 80 there is illustrated schematically and in blockdiagram form a laser system 1350 according to aspects of an embodimentof the disclosed subject matter. which may comprise a plurality of seedlasers 1352 a, 1352 b and 1352 c which may be solid state lasers, 1352a, 1352 b, 1352 c, for example as described elsewhere in the presentapplication, with the seed laser 1352 c being an nth seed laser in thesystem 1450. Each of the seed lasers may feed a pair of respectiveamplifier gain mediums 1356, 1358, 1360, 1362 and 1364, 1366, with theamplifier gain mediums 1364, 1366 being the nth pair in the system 1350,corresponding to the nth seed laser 1352 c, with a respective beamdivider 1354. Each amplification gain medium may be a gas dischargelaser, such as an excimer or molecular fluorine laser, and morespecifically may comprise a ring power amplification stage as describedelsewhere in the present application and in above identified co-pendingapplications filed on the same day as the present application. Each ofthe pairs of amplification gain mediums 1356, 1358, 1360, 1362, and1364, 1366 may operate at ½ the pulse repetition rate X of therespective seed laser 1252 a, 1352 b and 1352 c, with the seed lasers1352 a, 1352 b and 1352 c all operating at the same pulse repetitionrate X, to produce a laser light source output light beam of pulses 100at nX, or each may operate at a respective pulse repetition rate X, X′,X″ . . . X^(n′) some but not all of which may be equal to others, suchthat the output pulse rate in the output pulse beam 100 is ΣX′+X″ . . .X^(n), through a beam combiner 1370.

It will be understood by those skilled in the art that disclosed in thepresent application is a method and apparatus which may comprise a laserlight source system which may comprise a solid state laser seed beamsource providing a seed laser output; a frequency conversion stageconverting the seed laser output to a wavelength suitable for seeding anexcimer or molecular fluorine gas discharge laser, e.g., within a bandof wavelengths around the nominal center wavelength of the output of therespective type of gas discharge laser, which those skilled in the artwill understand to be able to be amplified in the selected gas dischargelasing medium; an excimer or molecular fluorine gas discharge laser gainmedium amplifying the converted seed laser output to produce a gasdischarge laser output at approximately the converted wavelength, whichthose skilled in the art will understand to be within the band ofwavelengths around a nominal center wavelength for the type of gasdischarge laser lasing medium, wherein seed laser pulses of theappropriate wavelength(s) will be amplified by stimulated emission inthe excited lasing medium. The excimer or molecular fluorine laser maybe selected from a group comprising XeCl, XeF, KrF, ArF and F₂ lasersystems. The laser gain medium may comprise a power amplifier. The poweramplifier may comprise a single pass amplifier stage, a multiple-passamplifier stage. The gain medium may comprise a ring power amplificationstage or a power oscillator. The ring power amplification stage maycomprise a bow-tie configuration or a race track configuration. Themethod and apparatus may further comprise an input/output coupler seedinject mechanism. The method and apparatus may further comprise acoherence busting mechanism. The solid state seed laser beam source maycomprise an Nd-based solid state laser, e.g., with an frequency doubledpump, pumping the Nd-based solid state laser. The Nd-based solid statelaser may comprise a fiber amplifier laser. The Nd-based solid statelaser may be selected from a group comprising: Nd:YAG, Nd:YLF andNd:YVO₄ solid state lasers. The solid state seed laser beam source maycomprise an Er-based solid state laser, e.g., comprising a fiber laser.The Er-based solid state laser may comprise an Er:YAG laser or, e.g., anEr:Glass laser. The frequency conversion stage may comprise a linearfrequency converter, e.g., may comprise a Ti:Sapphire crystal or maycomprise a crystal which may comprise Alexandrite. The frequencyconversion stage may comprise a non-linear frequency converter, e.g.,comprising a second harmonic generator or a sum-frequency mixer.

Applicants have simulated through calculations speckle reduction asrelates to the location of coherence lengths within a single gasdischarge (e.g., ArF or KrF excimer) laser system output pulse aftersuch a pulse has passed through the two OPuS pulse stretchers sold onlaser systems manufactured by applicants' assignee Cymer, Inc., used forpulse stretching to increase the total integrated spectrum (T_(is)) toreduce the impact of peak intensity in the laser output pulse on theoptics in the tool using the output light from the laser system, e.g., alithography tool scanner illuminator. There are two OPuS in series, withthe first having a delay path sufficient to stretch the T_(is) of theoutput pulse from about 18.6 ns to about 47.8 ns and the second tostretch the pulse further to about 83.5 ns, e.g., measured at E95% (thewidth of the spectrum within which is contained 95% of the energy of thepulse.

Starting with the unstretched pulse, applicants divided the pulse intoportions equal to the approximate coherence length, assuming a FWHMbandwidth of 0.10 pm and a Gaussian shape for the coherence lengthfunction. The impact of the pulse stretching on the coherence lengthportions of the pulse after passing through the first OPuS was to showthat a first intensity hump in the spectrum of the stretched pulse wasmade up of the coherence length portions of the main pulse, a secondintensity hump was mad up of coherence length portions of the main pulseoverlapped with coherence length portions of a first daughter pulse. Athird hump in the intensity spectrum is the result of overlapping of thefirst and second daughter pulses. Looking at the individual coherencelength portions of the two humps applicants observed that the multipleversions (including daughters) of the coherence length portions remainedsufficiently separated to not interfere with each other.

After passage through the second OPuS the simulated spectra, again onlylooking at the content of the first three humps in the stretched pulse,in the simulation (under the second hump were contributions from theoriginal undelayed pulse, as before, the first delayed pulse from thefirst OPuS, as before and the first delayed pulse from the second OPuS),applicants observed that in this second pulse the multiple versions ofthe coherence length portions were very close together. This is causedby the fact that the first OPuS has a delay of ˜18 ns and the second hasa delay of ˜22 ns. Thus only ˜4 ns separates the versions of thecoherence length portions, which is still not close enough forinterference.

Under the third hump applicants observed contributions from the firstdelayed pulse from the first OPuS, the second delayed pulse from firstOPuS, the first delayed pulse from the second OPuS, and the seconddelayed pulse from second OPuS. applicants observed that the separationbetween some related coherence portions is larger than for others in thethird hump in the intensity spectrum of the pulse stretched by twoOPuSs. This increase in separation is due to the fact that two roundtrips through each OPuS equal ˜36 ns=18*2 and ˜44 ns=22*2. Thus theseparation between coherence lengths grows with each round trip.

Applicants have determined that for each single mini-OPuS to beeffective, the two main OPuSs should not bring any daughter coherencelengths to within about 4 coherence lengths of each other. That is, toinsure that correlated temporal coherence elements do not overlap, theremust be taken into account the specification of the separate delay pathssuch that temporal coherence elements from the main beam are not laterrecombined with themselves through coincidence of the delayed version ofthe element due to the different delay paths. Such overlapping in timeby the effect of the various combinations of delay paths is undesirablefrom a speckle reduction standpoint.

Care must be taken with selection of the delay lengths of the mini-OPuSsand main OPuSs to avoid temporal collision of the temporal coherenceelements. According to aspects of an embodiment of the present inventionapplicants propose the coordinated change of the regular OPuS delaylengths when the mini-OPuS(s) are installed, including whether they arepart of the laser system or installed down stream of the regular mainOPuSs, e.g., in the lithography tool itself Applicants believe that suchmini-OPuS(s) can fill in the valleys of the pulse duration somewhat,leading to an increase in T_(is), e.g., allowing a reduction in thedelay lengths of one of the two main OPuSes for better overall coherencelength separation.

According to aspects of an embodiment of the disclosed subject matter,the coherence busting may be through a combination of delay paths andthe special means noted above, e.g., beam flipping, negative oneimaging, beam translation/shear, beam chirp or beam fan out, implementedas discussed above.

Turning now to FIGS. 81A-c there is shown perspectively and partlyschematically a ray trace for an embodiment of the disclosed subjectmatter comprising, e.g., a MO chamber 22 and an amplifier gain mediumchamber 144, with FIG. 81A showing the left hand portions of the tracedrays in the seed laser chamber 22 above and the amplifier gain mediumchamber 144 below. The beam leaves the line narrowing module LNM (notshown in FIG. 81A) through the LNM aperture 29 and enters the seed laserchamber 22 through the MO chamber rear window 28. At the left hand sideof the bow tie beam exits the amplification gain medium chamber 144through the rear window thereof 167, passes through a beam reverseraperture 71 and is reversed in the beam reverser 70 as explained aboveand returns to the amplification gain medium chamber 144 through theaperture 71 and window 167 on a slightly different path than the path tothe beam reverser/returner 70, in the exemplary case in a crossingarrangement forming the bow-tie.

Turning to FIG. 81B there is shown perspectively and partlyschematically a part of the relay optics and coherence busting delaypaths intermediate the seed laser chamber 22 and the amplification gainmedium chamber 144. the seed pulses output from the seed laser chamber22 in a seed laser output light pulse beam of pulses passes through theseed laser right hand window 27, an output coupler 28 and a LAM beamsplitter where, e.g., a portion of the beam is diverted for metrologypurposes. The beam is then turned horizontally and vertically in a pairof turning mirrors 44 a and 44 b and is directed to a beam splitter 526in a first mini-OPus delay path 376, e.g., a 3 ns delay path, with partof the beam, e.g., 40% reflected into the delay path and the remainderpassing into a second delay path 380. A compensator wedge 530, may bealigned to overlap the daughter pulses exiting the delay path 376 orslightly misaligned to give the respective daughter pulses a slightlydifferent spatial path on exit from the delay path 376 (beam shear). Thedelay path 376 may be formed by a pair of confocal mirrors 522, 524 orother mirror arrangements, including, e.g., two or more confocal ornon-confocal mirrors at each end of the delay path 376 delivering thedelayed beam back to the beam splitter 526. The beam can then pass intoa second delay path 380, e.g., a 4 ns delay path with a beam splitter526′ where a portion of the beam, e.g., 405 is reflected into the delaypath and the remainder passed out of the delay path 380 and into, e.g.,a beam expander 30. The delay path, except for having the differentdelay, e.g., 4 ns, may be constructed identically to that of the delaypath 376, or may be of a different variety, e.g., with a differentmirror configuration, e.g., arranged for beam flipping and/or negativeone imaging or the like. In lieu of the compensator plate that ismisaligned, the first or second delay paths 376, 380 may have one or theother aligned for output beam overlap, or may have one or the othersubstituted with a beam flipping optical element as discussed in moredetail elsewhere.

The beam exiting the second delay path may pass through a beam expander,e.g., a dual prism beam expander 30, e.g., including a first expandingprism 32 and a second expanding prism 30.

Turning now to FIG. 81 C there is illustrated the input/output couplingoptics and the laser system output beam optical path associated withinput of the seed laser beam leaving the beam expander 30 and enteringand leaving the amplification gain medium stage 144, e.g., in a bow-tiering power amplification stage arrangement. The beam leaving the beamexpander 30 is turned by a turning mirror 45 into a partially reflectivemirror 162 acting as a beam splitter/input/output coupler optic for theamplification gain medium stage 144. The partially reflective mirror 162may have an anti-reflective coating on the input incidence side and be,e.g./20-30% reflective on the opposite amplification gain medium chambercavity side, to perform the output coupler function. The partiallyreflective mirror passes the beam to a maximally reflective mirror (forthe given wavelength) which can reflect the beam into the amplificationgain medium chamber 144 through a beam expander optical assembly and achamber right side window 168. The beam expander optical arrangement mayinclude a first (input) beam expander prism portion 146 a and on to asecond beam expander prism 148 and into the amplification gain mediumchamber along a first path, while the returning beam in the, e.g.,bow-tie loop may pass through the second beam expander prism 148 andthrough a first beam expander prism second portion 146 b, which expandsthe amplified beam exiting through the input/output coupler 162 orreturning to the chamber through reflection off of the output coupler162 and maximally reflective mirror 164 in the bow-tie oscillation loop.

The beam exiting the amplification gain medium chamber 144 through theoutput coupler 162 may pass through a BAM beam splitter where a portionof the beam is redirected for metrology purposes, an OPUS beam splitterwhere the beam is separated into a main portion and a delayed portionthrough one of more main OPuSs for beam stretching to lengthen theT_(is) of the laser system output pulse, a system aperture 92 and ashutter beam splitter where a portion of the beam is separated out formetrology purposes.

Turning now to FIGS. 82A and 82B there is illustrated perspectively andpartly schematically a top view of a portion of the optical train ofFIGS. 81A-C, including the relay optics between the seed laser chamberand the amplification gain medium laser chamber. FIG. 83A shows aperspective and partly schematically a more detailed view of the delaypaths 376 and 380 and the beam expander 30. FIG. 83 B shows a side viewof more detail of the beam expander 30.

The design of the delay path, e.g., the 3 ns delay path may include a3.18 mm thick beam splitter 526, two concave mirrors 522, 524, e.g.,with a radius of curvature of 225 mm, and a compensator plate 530 sothat the reflected beams will overlap the transmitted beam. If thereflected/delayed beam is desired to not overlap the transmitted beam, anumber of embodiments may be employed, including, e.g., the tilting ofthe compensator plate 530. Thus, for example, with the an offset of thebeam going through the beam splitter 526 at 1.048 mm, the compensatorplate 530 may be placed at an opposite angle from that of the beamsplitter 526. The reflected beam will then overlap the transmitted beam.By changing the angle of rotation of the compensator plate 530, theoffset between the transmitted beam and the first reflected beam can becontrolled. If the beam splitter 526 is normal to the beam, the offsetbetween the two beams is 1.048 mm. The delta offset between the twobeams as a function of angle is shown in FIG. 85. To produce an offsetof 0.5 mm, an incidence angle of 27 degrees is needed. Another way toproduce the offset could be, e.g., to make the compensator plate 530thinner or thicker. A plate thickness of 1.66 or 4.70 mm will produce a0.5 mm offset. The advantage of using a thicker plate at 45 degrees isthat the anti-reflection coating stays the same. However, using a plateat 27 degrees uses the same thickness for the substrate as the beamsplitter 526. The beam incident on the compensator plate 530 iss-polarized, so it is better for the anti-reflection coating for thepart to be at 27 degrees rather than 45 degrees.

Additionally either delay path may be set up for one or more of thespecial means discussed elsewhere, of which the bean shearing techniquejust described may be one, with the other delay path, e.g., the 4 nsdelay path having the same or essentially the same beam manipulation(along with delay of a specified length) or may have a differentcoherence busting scheme. for Example as illustrated in FIG. 83schematically, the second, longer delay path, e.g., the 4 ns delay path380 may also incorporate a beam flipping mechanism, e.g., a prism suchas an isosceles prism 525, which, like the coherence busting opticsdisclosed in the co-pending patent application noted above entitledMETHOD AND APPARATUS FOR GAS DISCHARGE LASER OUTPUT LIGHT COHERENCYREDUCTION, filed on Dec. 29, 2005, Ser. No. 10/881,533, referencedabove, can, e.g., flip the beam upon itself in one or more axes. theexemplary beam flipping optic 525 may flip each daughter pulse onitself, e.g., in the long axis, as it passes through the prism andinternal reflections within the prism, as illustrated schematically inFIG. 86. As noted elsewhere, such coherence busting with delay a path orpaths and similar or assorted other special means for such as beamflipping, translation, imaging and the like as discussed elsewhere maybe done at the output of the amplification gain medium, intermediate theseed laser and amplification gain medium, after the laser systemshutter, in a beam delivery unit, e.g., an enclosed and absorptionspecies free beam path intermediate the laser shutter and the input tothe tool using the laser light or inside the tool itself, e.g., ascanner or a tbSLS machine.

It will be understood by those skilled in the art that an apparatus andmethod is disclosed that may comprise a line narrowed pulsed excimer ormolecular fluorine gas discharge laser system which may comprise a seedlaser oscillator producing an output comprising a laser output lightbeam of pulses which may comprise a first gas discharge excimer ormolecular fluorine laser chamber; a line narrowing module within a firstoscillator cavity; a laser amplification stage containing an amplifyinggain medium in a second gas discharge excimer or molecular fluorinelaser chamber receiving the output of the seed laser oscillator andamplifying the output of the seed laser oscillator to form a lasersystem output comprising a laser output light beam of pulses, which maycomprise a ring power amplification stage. The ring power amplificationstage may comprise an injection mechanism comprising a partiallyreflecting optical element through which the seed laser oscillatoroutput light beam is injected into the ring power amplification stage.The ring power amplification stage may comprise a bow-tie loop or a racetrack loop. The ring power amplification stage may amplify the output ofthe seed laser oscillator cavity to a pulse energy of ≧1 mJ or ≧2 mJ or≧5 mJ or ≧10 mJ or ≧15 mJ. The laser system may operate at an outputpulse repetition rate of up to 12 kHz, ≧2 and ≦8 kHz or ≧4 and ≦6 kHz.The apparatus and method may comprise a broad band pulsed excimer ormolecular fluorine gas discharge laser system which may comprise a seedlaser oscillator producing an output comprising a laser output lightbeam of pulses which may comprise a first gas discharge excimer ormolecular fluorine laser chamber; a laser amplification stage which maycontain an amplifying gain medium in a second gas discharge excimer ormolecular fluorine laser chamber receiving the output of the seed laseroscillator and amplifying the output of the seed laser oscillator toform a laser system output comprising a laser output light beam ofpulses, which may comprise a ring power amplification stage. Accordingto aspects of an embodiment of the disclosed subject matter a coherencebusting mechanism may be located intermediate the seed laser oscillatorand the amplifier gain medium. The coherence busting mechanism maycomprise an optical delay path having a delay length longer than thecoherence length of a pulse in the seed laser oscillator laser outputlight beam of pulses. The optical delay path may not substantiallyincrease the length of the pulse in the seed laser oscillator laseroutput light beam of pulses. The coherence busting mechanism maycomprise a first optical delay path of a first length and a secondoptical delay path of a second length, with the optical delay in each ofthe first and second delay paths exceeding the coherence length of apulse in the seed laser oscillator laser output light beam of pulses,but not substantially increasing the length of the pulse, and thedifference in the length of the first delay path and the second delaypath exceeding the coherence length of the pulse and also notsubstantially increasing the length of the pulse. The apparatus andmethod according to aspects of an embodiment may comprise a linenarrowed pulsed excimer or molecular fluorine gas discharge laser systemwhich may comprise a seed laser oscillator producing an outputcomprising a laser output light beam of pulses which may comprise afirst gas discharge excimer or molecular fluorine laser chamber; a linenarrowing module within a first oscillator cavity; a laser amplificationstage containing an amplifying gain medium in a second gas dischargeexcimer or molecular fluorine laser chamber receiving the output of theseed laser oscillator and amplifying the output of the seed laseroscillator to form a laser system output comprising a laser output lightbeam of pulses, which may comprise a ring power amplification stage; acoherence busting mechanism intermediate the seed laser oscillator andthe ring power amplification stage. According to aspects of anembodiment the apparatus and method may comprise a broad band pulsedexcimer or molecular fluorine gas discharge laser system which maycomprise a seed laser oscillator producing an output comprising a laseroutput light beam of pulses which may comprise a first gas dischargeexcimer or molecular fluorine laser chamber; a laser amplification stagecontaining an amplifying gain medium in a second gas discharge excimeror molecular fluorine laser chamber receiving the output of the seedlaser oscillator and amplifying the output of the seed laser oscillatorto form a laser system output comprising a laser output light beam ofpulses, which may comprise a ring power amplification stage; a coherencebusting mechanism intermediate the seed laser oscillator and the ringpower amplification stage. The apparatus and method according to aspectsof an embodiment may comprise a pulsed excimer or molecular fluorine gasdischarge laser system which may comprise a seed laser oscillatorproducing an output comprising a laser output light beam of pulses whichmay comprise a first gas discharge excimer or molecular fluorine laserchamber; a line narrowing module within a first oscillator cavity; alaser amplification stage containing an amplifying gain medium in asecond gas discharge excimer or molecular fluorine laser chamberreceiving the output of the seed laser oscillator and amplifying theoutput of the seed laser oscillator to form a laser system outputcomprising a laser output light beam of pulses; a coherence bustingmechanism intermediate the seed laser oscillator and the laseramplification stage comprising an optical delay path exceeding thecoherence length of the seed laser output light beam pulses. Theamplification stage may comprise a laser oscillation cavity or anoptical path defining a fixed number of passes through the amplifyinggain medium. The coherence busting mechanism may comprise comprising acoherence busting optical delay structure generating multiple sub-pulsesdelayed sequentially from a single input pulse, wherein each sub-pulseis delayed from the following sub-pulse by more than the coherencelength of the pulse light. It will also be understood by those skilledin the art that an apparatus and method is disclosed which may compriseaccording to aspects of an embodiment a laser light source system whichmay comprise a solid state laser seed beam source providing a seed laseroutput; a frequency conversion stage converting the seed laser output toa wavelength suitable for seeding an excimer or molecular fluorine gasdischarge laser; an excimer or molecular fluorine gas discharge lasergain medium amplifying the converted seed laser output to produce a gasdischarge laser output beam of pulses at approximately the convertedwavelength; a coherence busting mechanism comprising an optical delayelement having a delay path longer than the coherence length of theoutput pulse. The excimer or molecular fluorine laser may be selectedfrom a group comprising XeCl, XeF, KrF, ArF and F₂ laser systems. Thelaser gain medium may comprise a power amplifier, which may comprise asingle pass amplifier stage or a multiple-pass amplifier stage. The gainmedium may comprise a ring power amplification stage, which may comprisea bow-tie configuration or race track configuration and may alsocomprise an input/output coupler seed inject mechanism. The coherencebusting mechanism may be intermediate the laser seed beam source and thegas discharge laser gain medium. The solid state seed laser beam sourcemay comprise an Nd-based solid state laser and may comprise a frequencydoubled pump pumping the Nd-based solid state laser. The Nd-based solidstate laser may comprise a fiber amplifier laser and may comprise anNd-based solid state laser selected from a group which may compriseNd:YAG, Nd:YLF and Nd:YVO₄ solid state lasers. The solid state seedlaser beam source may comprise an Er-based solid state laser, which maycomprise a fiber laser. The Er-based solid state laser may comprise anEr:YAG laser. The frequency conversion stage may comprise a linearfrequency converter, which may comprise a Ti:Sapphire crystal or acrystal comprising Alexandrite. The frequency conversion stage maycomprise a non-linear frequency converter, e.g., a second harmonicgenerator or a sum-frequency mixer. The apparatus and method accordingto aspects of an embodiment may comprise a laser light source systemwhich may comprise a solid state laser seed beam source providing a seedlaser output; frequency conversion stage converting the seed laseroutput to a wavelength suitable for seeding an excimer or molecularfluorine gas discharge laser; an excimer or molecular fluorine gasdischarge laser gain medium amplifying the converted seed laser outputto produce a gas discharge laser output at approximately the convertedwavelength, which may comprise a ring power amplification stage. Themethod may comprise utilizing a solid state laser seed beam source toprovide a seed laser output; frequency converting in a frequencyconversion stage the seed laser output to a wavelength suitable forseeding an excimer or molecular fluorine gas discharge laser; utilizingan excimer or molecular fluorine gas discharge laser gain medium,amplifying the converted seed laser output to produce a gas dischargelaser output at approximately the converted wavelength.

It will also be understood by those skilled in the art that an apparatusand method is disclosed that may comprise a processing machine which maycomprise an irradiation mechanism irradiating a workpiece, such as asemiconductor manufacturing wafer or a thin film transistor panel beingirradiated, e.g., as part of a photolithography process in the formercase and laser annealing for amorphous silicon crystallization in thelatter, with pulsed UV light, e.g., DUV light, e.g., at 248 nm or 193nm, or EUV light, e.g., at around 13 nm; a UV light input opening; aworkpiece holding platform, e.g., a wafer transfer stage or a thin filmpanel transfer stage; a coherence busting mechanism comprising anoptical delay path exceeding the coherence length of the UV lightpulses. The optical delay path may not substantially increase the lengthof the UV light pulse. The coherence busting mechanism may comprise afirst optical delay path of a first length and a second optical delaypath of a second length, with the optical delay in each of the first andsecond delay paths exceeding the coherence length of the UV light pulse,but not substantially increasing the length of the pulse, and thedifference in the length of the first delay path and the second delaypath exceeding the coherence length of the pulse. At least one of thefirst and second optical delay paths may comprise a beam flipping orbeam translating mechanism, e.g., the misaligned compensator plate,flipping optical elements, negative on e imaging optical elements andthe like.

It will be understood by those skilled in the art that the aspects ofembodiments of the disclosed subject matter disclosed above are intendedto be preferred embodiments only and not to limit the disclosure of thedisclosed subject matter(s) in any way and particularly not to aspecific preferred embodiment alone. Many changes and modification canbe made to the disclosed aspects of embodiments of the disclosedinvention(s) that will be understood and appreciated by those skilled inthe art. The appended claims are intended in scope and meaning to covernot only the disclosed aspects of embodiments of the disclosed subjectmatter(s) but also such equivalents and other modifications and changesthat would be apparent to those skilled in the art. In additions tochanges and modifications to the disclosed and claimed aspects ofembodiments of the disclosed subject matter(s) noted above others couldbe implemented.

While the particular aspects of embodiment(s) of the LASER SYSTEMdescribed and illustrated in this patent application in the detailrequired to satisfy 35 U.S.C. §112 is fully capable of attaining anyabove-described purposes for, problems to be solved by or any otherreasons for or objects of the aspects of an embodiment(s) abovedescribed, it is to be understood by those skilled in the art that it isthe presently described aspects of the described embodiment(s) of thesubject matter disclosed are merely exemplary, illustrative andrepresentative of the subject matter which is broadly contemplated bythe subject matter disclosed. The scope of the presently described andclaimed aspects of embodiments fully encompasses other embodiments whichmay now be or may become obvious to those skilled in the art based onthe teachings of the Specification. The scope of the present LASERSYSTEM is solely and completely limited by only the appended claims andnothing beyond the recitations of the appended claims. Reference to anelement in such claims in the singular is not intended to mean nor shallit mean in interpreting such claim element “one and only one” unlessexplicitly so stated, but rather “one or more”. All structural andfunctional equivalents to any of the elements of the above-describedaspects of an embodiment(s) that are known or later come to be known tothose of ordinary skill in the art are expressly incorporated herein byreference and are intended to be encompassed by the present claims. Anyterm used in the specification and/or in the claims and expressly givena meaning in the Specification and/or claims in the present applicationshall have that meaning, regardless of any dictionary or other commonlyused meaning for such a term. It is not intended or necessary for adevice or method discussed in the Specification as any aspect of anembodiment to address each and every problem sought to be solved by theaspects of embodiments disclosed in this application, for it to beencompassed by the present claims. No element, component, or method stepin the present disclosure is intended to be dedicated to the publicregardless of whether the element, component, or method step isexplicitly recited in the claims. No claim element in the appendedclaims is to be construed under the provisions of 35 U.S.C. §112, sixthparagraph, unless the element is expressly recited using the phrase“means for” or, in the case of a method claim, the element is recited asa “step” instead of an “act”.

It will be understood also be those skilled in the art that, infulfillment of the patent statutes of the United States, applicant(s)has disclosed at least one enabling and working embodiment of eachinvention recited in any respective claim appended to the Specificationin the present application and perhaps in some cases only one. Forpurposes of cutting down on patent application length and drafting timeand making the present patent application more readable to theinventor(s) and others, applicant(s) has used from time to time orthroughout the present application definitive verbs (e.g., “is”, “are”,“does”, “has”, “includes” or the like) and/or other definitive verbs(e.g., “produces,” “causes” “samples,” “reads,” “signals” or the like)and/or gerunds (e.g., “producing,” “using,” “taking,” “keeping,”“making,” “determining,” “measuring,” “calculating” or the like), indefining an aspect/feature/element of, an action of or functionality of,and/or describing any other definition of an aspect/feature/element ofan embodiment of the subject matter being disclosed. Wherever any suchdefinitive word or phrase or the like is used to describe anaspect/feature/element of any of the one or more embodiments disclosedherein, i.e., any feature, element, system, sub-system, component,sub-component, process or algorithm step, particular material, or thelike, it should be read, for purposes of interpreting the scope of thesubject matter of what applicant(s) has invented, and claimed, to bepreceded by one or more, or all, of the following limiting phrases, “byway of example,” “for example,” “as an example,” “illustratively only,”“by way of illustration only,” etc., and/or to include any one or more,or all, of the phrases “may be,” “can be”, “might be,” “could be” andthe like. All such features, elements, steps, materials and the likeshould be considered to be described only as a possible aspect of theone or more disclosed embodiments and not as the sole possibleimplementation of any one or more aspects/features/elements of anyembodiments and/or the sole possible embodiment of the subject matter ofwhat is claimed, even if, in fulfillment of the requirements of thepatent statutes, applicant(s) has disclosed only a single enablingexample of any such aspect/feature/element of an embodiment or of anyembodiment of the subject matter of what is claimed. Unless expresslyand specifically so stated in the present application or the prosecutionof this application, that applicant(s) believes that a particularaspect/feature/element of any disclosed embodiment or any particulardisclosed embodiment of the subject matter of what is claimed, amountsto the one an only way to implement the subject matter of what isclaimed or any aspect/feature/element recited in any such claim,applicant(s) does not intend that any description of any disclosedaspect/feature/element of any disclosed embodiment of the subject matterof what is claimed in the present patent application or the entireembodiment shall be interpreted to be such one and only way to implementthe subject matter of what is claimed or any aspect/feature/elementthereof, and to thus limit any claim which is broad enough to cover anysuch disclosed implementation along with other possible implementationsof the subject matter of what is claimed, to such disclosedaspect/feature/element of such disclosed embodiment or such disclosedembodiment. Applicant(s) specifically, expressly and unequivocallyintends that any claim that has depending from it a dependent claim withany further detail of any aspect/feature/element, step, or the like ofthe subject matter of what is claimed recited in the parent claim orclaims from which it directly or indirectly depends, shall beinterpreted to mean that the recitation in the parent claim(s) was broadenough to cover the further detail in the dependent claim along withother implementations and that the further detail was not the only wayto implement the aspect/feature/element claimed in any such parentclaim(s), and thus be limited to the further detail of any suchaspect/feature/element recited in any such dependent claim to in any waylimit the scope of the broader aspect/feature/element of any such parentclaim, including by incorporating the further detail of the dependentclaim into the parent claim.

It will be understood by those skilled in the art that the aspects ofembodiments of the subject matter disclosed above are intended to bepreferred embodiments only and not to limit the disclosure of thesubject matter disclosed(s) in any way and particularly not to aspecific preferred embodiment alone. Many changes and modification canbe made to the disclosed aspects of embodiments of the disclosed subjectmatter disclosed(s) that will be understood and appreciated by thoseskilled in the art. The appended claims are intended in scope andmeaning to cover not only the disclosed aspects of embodiments of thesubject matter disclosed(s) but also such equivalents and othermodifications and changes that would be apparent to those skilled in theart. In additions to changes and modifications to the disclosed andclaimed aspects of embodiments of the subject matter disclosed(s) notedabove others could be implemented.

We claim:
 1. A method of operating a pulsed gas discharge laser system,the method comprising: producing, at a seed laser oscillator including afirst gas discharge laser chamber, an output comprising a laser outputlight beam of pulses; directing the output produced at the seed laseroscillator through a regenerative ring power amplification stagecontaining an amplifying gain medium in a second gas discharge laserchamber; amplifying the produced output within the regenerative ringpower amplification stage to thereby form a laser system outputcomprising a laser output light beam of pulses, the regenerative ringpower amplification stage comprising a closed optical cavity defined inpart by a partially reflecting optical element through which the seedlaser oscillator output light beam is injected and through which thelaser system output is transmitted, the partially reflecting opticalelement being a single piece and comprising portions that are angledrelative to each other; selecting a differential timing between anelectrical discharge between a pair of electrodes in the first laserchamber and a pair of electrodes in the second laser chamber to therebymaintain amplified spontaneous emission below a selected limit and thepulse energy of the laser system output light beam of pulses essentiallyconstant; and actively tuning the bandwidth of the pulses of the seedlaser output light beam of pulses, wherein tuning the bandwidthcomprises adjusting an interaction of a pulse wavefront with a bandwidthselection optic in a line narrowing module of the seed laser oscillator.2. The method of claim 1, wherein: selecting the differential timingenables control of the bandwidth of the pulses in the laser output lightbeam of pulses.
 3. The method of claim 1, wherein: the bandwidthselection optic comprises a grating; and adjusting the interactioncomprises changing the shape of a face of the grating upon which isincident the pulse.
 4. The method of claim 1, wherein: the bandwidthselection optic comprises a grating; and adjusting the interactioncomprises changing the shape of the wavefront of the pulse incident onthe grating.
 5. The method of claim 1, wherein: the bandwidth selectionoptic comprises a grating; and adjusting the interaction compriseschanging the shape of a face of the grating upon which is incident thepulse and changing the shape of the wavefront of the pulse incident onthe grating.
 6. The method of claim 1, wherein the partially reflectingoptical element further comprises a portion that is maximally reflectiveto a nominal center wavelength that propagates in the ring poweramplification stage.
 7. A method of operating a pulsed gas dischargelaser system, the method comprising: producing, at a seed laseroscillator including a first gas discharge laser chamber, an outputcomprising a laser output light beam of pulses; directing the outputproduced at the seed laser oscillator through a regenerative ring poweramplifier stage containing an amplifying gain medium in a second gasdischarge laser chamber; amplifying the produced output within theregenerative ring power amplification stage to thereby form a lasersystem output comprising a laser output light beam of pulses, theregenerative ring power amplification stage comprising a closed opticalcavity defined in part by a partially reflecting optical element throughwhich the seed laser oscillator output light beam is injected andthrough which the laser system output is transmitted, the partiallyreflecting optical element being a single piece and comprising portionsthat are angled relative to each other; selecting a differential timingbetween an electrical discharge between a pair of electrodes in thefirst laser chamber and a pair of electrodes in the second laser chamberto thereby enable control of the bandwidth of the pulses in the laseroutput light beam of pulses; and tuning the bandwidth of the pulses ofthe seed laser output light beam of pulses, wherein tuning the bandwidthcomprises adjusting an interaction of a pulse wavefront with a bandwidthselection optic in a line narrowing module of the seed laser oscillator.8. The method of claim 7, wherein: the bandwidth selection opticcomprises a grating; and adjusting the interaction comprises changingthe shape of a face of the grating upon which is incident the pulse. 9.The method of claim 7, wherein: the bandwidth selection optic comprisesa grating; and adjusting the interaction comprises changing the shape ofthe wavefront of the pulse incident on the grating.
 10. The method ofclaim 7, wherein: the bandwidth selection optic comprises a grating; andadjusting the interaction comprises changing the shape of a face of thegrating upon which is incident the pulse and changing the shape of thewavefront of the pulse incident on the grating.
 11. A method ofoperating a pulsed gas discharge laser system, the method comprising:producing, at a seed laser oscillator including a first gas dischargelaser chamber, an output comprising a laser output light beam of pulses;directing the output produced at the seed laser oscillator through aregenerative ring power amplification stage containing an amplifyinggain medium in a second gas discharge laser chamber; amplifying theproduced output within the regenerative ring power amplification stageto thereby form a laser system output comprising a laser output lightbeam of pulses, the regenerative ring power amplification stagecomprising a closed optical cavity defined in part by a partiallyreflecting optical element through which the seed laser oscillatoroutput light beam is injected and through which the laser system outputis transmitted, the partially reflecting optical element being a singlepiece and comprising portions that are angled relative to each other;selecting a differential timing between an electrical discharge betweena pair of electrodes in the first laser chamber and a pair of electrodesin the second laser chamber; and actively tuning the bandwidth of thepulses of the seed laser output light beam of pulses, wherein tuning thebandwidth comprises adjusting an interaction of a pulse wavefront with abandwidth selection mechanism in a line narrowing module of the seedlaser oscillator.
 12. The method of claim 11, wherein: the bandwidthselection mechanism comprises a grating; and adjusting the interactioncomprises changing the shape of a face of the grating upon which isincident the pulse.
 13. The method of claim 11, wherein: the bandwidthselection mechanism comprises a grating; and adjusting the interactioncomprises changing the shape of the wavefront of the pulse incident onthe grating.
 14. An apparatus comprising: a pulsed gas discharge lasersystem comprising a seed laser oscillator producing an output comprisinga laser output light beam of pulses comprising a first gas dischargelaser chamber; a regenerative ring laser amplification stage containingan amplifying gain medium in a second gas discharge laser chamberreceiving the output of the seed laser oscillator and amplifying theoutput of the seed laser oscillator to form a laser system outputcomprising a laser output light beam of pulses, the regenerative ringlaser amplification stage comprising a closed optical cavity defined inpart by a partially reflecting optical element through which the seedlaser oscillator output light beam is injected and through which thelaser system output is transmitted, the partially reflecting opticalelement being a single piece and comprising portions that are angledrelative to each other; and a timing and energy controller selecting adifferential timing between an electrical discharge between a pair ofelectrodes in the first laser chamber and a pair of electrodes in thesecond laser chamber to thereby keep amplified spontaneous emissionbelow a selected limit and the pulse energy of the laser system outputlight beam of pulses essentially constant, wherein a line narrowingmodule includes a bandwidth selection optic that is connected to thetiming and energy controller to enable the controller to adjust thebandwidth of the seed laser oscillator output beam.
 15. The apparatus ofclaim 14, wherein the seed laser oscillator includes a line narrowingmodule that includes a bandwidth selection mechanism.
 16. The apparatusof claim 14, wherein the ring laser amplification stage comprises abow-tie loop.
 17. The apparatus of claim 14, wherein the ring laseramplification stage comprises a race track loop.